They all happen after the Logging into Steam game server account step.
Error 1: common
Logging into Steam game server account
corrupted double-linked list
Error 2: uncommon
Logging into Steam game server account
malloc(): invalid size (unsorted)
These aren't inherently Box64 errors, but the way they put it it sounds that is very much the case.
I am unsure how to fix them as they are very general. Can somebody reproduce it and confirm it isn't just me?