I figured out my issue is caused by Bitdefender antivirus, specifically the “exploit detection” option within “advanced threat defense”.
No idea why that was causing the crash since it doesn’t appear as a logged event, and adding every relevant application as an exception did nothing. But on the off chance anyone has the same issue with that antivirus, turning off “exploit detection” allows me to connect, and turning it back on once a first connection is established for the session causes no other issues. Doesn’t explain how one time the first connection was established in a private game with someone who wasn’t on my friends list while the problematic antivirus setting was on, but oh well.