Thanks, I was able to connect to the server and reproduce the problem. It appears the pure list (sv_paks) is not being set correctly on the server, due to an overflow from too many pk3s. Specifically, I suspect the BIG_INFO_STRING limit is being hit in Info_SetValueForKey_Big on sv_paks, preventing it from being placed in the systeminfo.
As for why the test builds failed to connect while older versions succeeded, it might be related to the newer versions being more eager to load qvm files outside of pk3s, which causes the pure verfication check to fail. When I ran the test builds with the baseq3/vm folder (that comes from the test build zip) excluded, I was able to connect to the server like with the old versions.
The overall solution to the problem is to set sv_pure to 0 on the server, or have a smaller number of paks on the server. This should probably also be addressed as a bug in ioq3, since there should be better checks and handling of this kind of overflow.