[Sappykun]

Two months later, but an update:

The crash was caused by calling TF2_RespawnPlayer inside a SetTransmit hook. Changing that to use RequestFrame instead fixed the issue for me.
I've attached an updated version of the plugin to address the issues I mentioned above, plus some compiler warnings I was getting when building the plugin myself (warning 242: function "Timer_AverageUpdateRespawnTime" should return an explicit value, etc.)

Special thanks to bakugo for finding the fix.