[Bug] Switching accounts hangs forever after Minecraft has been opened for a while

[VidTu]

People on Discord have reported that it hangs IAS thread (not main client thread) either while "Initializing..." (which may be a result of trying to access already frozen thread) or when trying to flush the credentials ("Finalizing"), which is probably caused by some Mojang stuff.

There's no exact way to reproduce this, but it's worth looking into.

Possible ways to reproduce:

• Having MC open for a long time.
• Unplugging the internet at random, at Minecraft launching, at account switching, before finalizing, etc.