On server authority, some sessions join in a degraded state where the client receives server data at a fraction of the normal rate, and it stays that way for the entire session. Rejoining the same server fixes it but is not an acceptable solution for a competitive game. It’s decided per connection at join: two PCs on ethernet on the same LAN, in the same server, can get one degraded and one healthy client at the same time. This has been happening since at least Aug 26, 2026; the measurements below are from Aug 26-27 (EDT).
What it looks like in game, one of two ways:
Degraded: https://videos.mageml.com/shaky.mp4
Smooth: https://videos.mageml.com/smooth.mp4
- the player’s own predicted movement vibrates (constant frame over frame direction reversals from late corrections)
- the character repeatedly freezes for ~300ms while walking, with fps locked at 240, so it’s not a client hitch
Numbers from per-frame probes (2s windows, 240fps client). These print to the developer console live, so you can watch them in F9 while reproducing — the [netdiag] lines:
- healthy session: 0-1 motion reversals per window during fast WASD direction changes, longest position stall 4ms, inbound ~22-31 KB/s while moving
- degraded session, same hardware: 17-39 reversals per window (or the ~300ms freezes), inbound drops to 2-6 KB/s while moving. Idle bursts still hit 150 KB/s in the same degraded session, so it’s not a bandwidth cap.
- ping 3-20ms, physics 60Hz, server heartbeat ~60Hz in every capture
Cycling SetPredictionMode off and back on mid session does not recover it. Only reconnecting does.
Repro:
- Join MageBrawl on a live server (can do this solo): MageBrawl | Play on Roblox
- Step on the blue solo practice pad to start the practice match.
- Each time you get teleported there’s a chance your session arrives in the degraded state.
- To check after each teleport: spam WASD back and forth. Healthy sessions look smooth, degraded ones make your own character vibrate like an earthquake.
- If it is not degraded, press F2 to exit practice and repeat steps 2-4 until it shows up, usually only takes a handful of tries.
OR if you want to teset with more than one person:
- Join MageBrawl on a live server: MageBrawl | Play on Roblox (you need enough players for a match, 2 for 1v1 or 4 for 2v2) (You can use a second computer and just have them stand there, or I can help you replicate it if needed)
- Step on the 1v1 or 2v2 pad to start a match and play it out. Someone has to win the best of 3 for you to get teleported back to the lobby, so just kill each other quickly.
- Each time you get teleported there’s a chance your session arrives in the degraded state.
- To check after each teleport: spam WASD back and forth. Healthy sessions look smooth, degraded ones make your own character vibrate like an earthquake.
- Repeat matches until it shows up, usually only takes a handful.
Windows 11 Home (build 26200), AMD Ryzen 7 8700F, NVIDIA RTX 5070, 32 GB RAM, ethernet
Please help this bug is legitimately fatal for match based competitive games
Expected behavior
Every connection should receive the server’s authoritative state at the normal rate. If a connection ends up in a bad state, it should recover during the session instead of persisting until a rejoin.
A private message is associated with this bug report
