[T5MP] Dedicated server loops "SESSION CREATE ERROR 2103" (BD_INVALID_SESSION_ID) heartbeat OK, DW auth OK

[snrgabe]

Setup
T5MP dedicated server r5334 on Linux (Debian, Wine 9.0, Docker), game files from my own Steam copy (app 42700, Windows depot). Launched via:

bin/plutonium-bootstrapper-win32.exe t5mp /path/to/Server/ -dedicated +set key XXX +set fs_game "" +set net_port 21892 +exec dedicated.cfg +map_rotate

The server boots fine: fastfiles load, dedicated.cfg execs, map rotation set, DW auth completes (DW_AUTHORIZED -> DW_LOGON_COMPLETE), and heartbeats succeed. But it endlessly loops:

Parsed 0 reserved slot passwords
SESSION CREATE ERROR 2103
Session creation failed. Killing server
MATCHMAKINGDEBUG: Calling updatesession...
Server: Updating session - serverinfo change
Session update error!

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RECREATING SESSION

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reauthenticating dedicated server!
DW_AUTHORIZED -> DW_LOGON_COMPLETE
SESSION CREATE ERROR 2103 (repeats forever)

2103 = 0x837 = BD_INVALID_SESSION_ID.

Already tried:

• Fresh server key created specifically for T5MP (not reused from another game)
• Removing all custom dvars from the launch line
• Fresh Plutonium files via plutonium-updater (r5334)

A T6MP server on the same host/network works perfectly (heartbeat, listing, players joining), so outbound connectivity and NAT are fine. Game UDP port is forwarded.

Is error 2103 on session create a known backend issue for T5MP dedis (similar to the old T5SP session errors), or is there something server-side I should check? Does this affect joinability/listing, or is it safe to ignore?