# Proxy session retry vs rotate: four 504s on one token > On a sticky residential proxy a session token is an exit, so retrying it asks a dead exit three more times. Rotate to a fresh session instead. Source: https://mosaicbrowser.com/blog/rotate-dont-retry ## Four 504s on one session: rotate, don't retry On a sticky residential proxy a session token is an exit, so retrying it asks a dead exit three more times. Rotate to a fresh session instead. ![504: Four 504s on one session, then a fresh one](https://mosaicbrowser.com/covers/rotate-dont-retry.webp) Retrying a failed proxy session and rotating to a new one are different questions on a sticky residential gateway. The session token in the username decides which exit you get, so a retry sends the same token to the same dead exit. A rotation mints a new token and asks for a different exit. Mosaic used to retry. It now rotates, and only when the session was its own to replace. ## The report: a red launch under a green provider The bug came in as a screenshot. A launch was refused four times with "The proxy gate-eu… did not answer … Proxy returned HTTP 504". A few centimetres above it, the provider's own status dot was green. The person who sent it put it plainly: they knew the proxy worked, and the app seemed to know it too. Both readings were true. The provider check and the launch were talking to the same gateway on two different sessions, so they reached two different exits. The check's session worked. The profile's session did not. ## Retry or rotate a proxy session? Mosaic checks a proxy before every launch, and that check has retried three times since a residential pool was first pointed at it, because one observation of somebody else's network is not evidence. The retry was sound for a gateway that hiccups. It was useless here, because all three attempts carried the same session token, and on a sticky endpoint a session token *is* an exit. To see how often this happens, we asked the seller for forty fresh sessions in a row. The twenty-ninth was dead: ``` session 889053 → 504 the attempt the launch refused on session 889053 → 504 retry 1, as it was written session 889053 → 504 retry 2 session 889053 → 504 retry 3 session 758767 → 504 a fresh one, also bad session 195609 → 200 session 131797 → 200 ``` A 504 there belongs to the session, not to the gateway. Three more tries on 889053 could only ever say 504 again. One new token was all it took, and the second new one answered. Mosaic is a desktop app Email yourself the link and open it on your computer. [How it works: Provider minting](https://mosaicbrowser.com/features/proxy-providers) ## What a rotation is allowed to move A failure now costs a different exit instead of a longer wait. But moving somebody's exit is a decision, so the rule is narrow. Mosaic rotates a session in two cases: - **The session was minted from a provider.** Every profile made from a provider holds a token Mosaic minted for it. The replacement is minted from the same provider with the same pick, so a profile asked for Germany gets another German exit. The token is written in the seller's own grammar, read off the gateway line you pasted, because a token we invented would authenticate and then be ignored. - **The proxy is marked to rotate on every launch.** There, the operator has already said the session is disposable. A session somebody pinned by hand is never moved. Quietly relocating it would be the silent repair this codebase refuses everywhere else: the profile would come out somewhere it was not asked to be, and nothing would say so. In that case the launch stops and the message names the proxy and quotes the gateway. When a rotation works on a provider-minted proxy, the new token is written back to the profile. Otherwise every later launch would start by failing on the dead one again. A rotate-on-launch token is never written back, because storing it is what would stop it rotating. ## Proving it without waiting for a bad exit A real pool will not fail on demand, so the end-to-end check uses a stub gateway that answers 504 for one named session and forwards every other. Both halves in one run: ``` A1. session the profile holds, killed at the gateway: 33396200 A2. start: running A3. session it holds now: 90537583 proxy gate: the first session did not answer, retried on a fresh one B1. a session pinned by hand, killed the same way: 77777777 B2. start: refused, correctly ``` The rule is written once and walked by `check:rotate` at all three places that mint a session: the launch, the provider check, and creating profiles from a provider. The last one matters most. One dead sample there would have left a whole batch drawn for no exit at all, the same kind of mismatch we wrote up in [a profile that claimed New York from Austria](https://mosaicbrowser.com/blog/austria-claimed-new-york). ## One small thing that made the refusal read like a bug The refusal quotes the gateway's own reason, and gateways do not punctuate. Our sentence ran straight into theirs: "Proxy returned HTTP 504 Launching anyway would open a browser…". A message doing its job read like a broken one. The quoted reason now gets its full stop before our sentence begins. ## If you run residential proxies anywhere The lesson is not specific to Mosaic. When a [residential proxy](https://mosaicbrowser.com/glossary/residential-proxy) session fails, ask which part failed before retrying. A timeout or a refused connection can be the gateway; a 504 on one session while others answer is that session's exit. Retry the gateway; replace the session. Checking that a proxy answers *and* tunnels before you trust it is covered step by step in [how to check a proxy before you use it](https://mosaicbrowser.com/guides/how-to-check-a-proxy-before-you-use-it). In Mosaic, the provider side of this, one pasted gateway line that mints a separate session for every profile, is on [proxy providers](https://mosaicbrowser.com/features/proxy-providers). ## Questions ### Should I retry a proxy session that failed or rotate to a new one? On a sticky residential gateway, rotate. The session token decides the exit, so a retry on the same token asks the same dead exit again. In our run, one bad session answered 504 four times in a row while fresh sessions answered 200. ### Does a 504 from a residential proxy mean the whole gateway is down? Usually not. It can be one session's exit that reaches nothing. Mosaic's provider check mints its own session, which is why a provider can show green while one profile's session fails. ### Will Mosaic move a session I pinned by hand? No. Mosaic only replaces sessions it minted from a provider, or ones marked to rotate on every launch. A pinned session that fails stops the launch and the refusal quotes the gateway's reason. ### Does a rotated session keep the same country? Yes. The replacement is minted from the same provider with the same pick, so a profile asked for Germany gets another German session. ## Related [Provider accounts: one gateway line, one exit per profile](https://mosaicbrowser.com/features/proxy-providers): Paste your proxy seller's gateway line once and Mosaic mints a separate session for every profile, so each one browses from its own exit address. [How to check a proxy before you use it](https://mosaicbrowser.com/guides/how-to-check-a-proxy-before-you-use-it): Check that a proxy answers and tunnels, where its exit really is, whether the address is residential or blocklisted, and that the browser stays behind it. [Residential proxy: an exit on a home internet connection](https://mosaicbrowser.com/glossary/residential-proxy): A residential proxy sends your traffic out through an address an ISP assigned to a home connection, so sites see a household rather than a data center. [A profile in Austria claimed New York](https://mosaicbrowser.com/blog/austria-claimed-new-york): Browser location does not match IP: a no-proxy profile made in Austria claimed New York. One failed lookup was never retried, and a table filled the gap.   [Same proxy session on multiple profiles: forty profiles, forty exits](https://mosaicbrowser.com/blog/forty-profiles-forty-exits): The same proxy session on multiple profiles means one exit IP for all of them. A batch of ours did it in September 2026; now every profile mints its own.  ## Mosaic, on your own computer The browser this blog is about: its own Chromium, fingerprints from real machines and a proxy exit per profile. Free holds 3 profiles. Pro is $49 a month for any number. Mosaic is a desktop app Email yourself the link and open it on your computer.