Thanks for your report. I assume you are talking about Audio sync (auto) based on timecode.
Are you able to provide some details on what type of video/audio files you are syncing? Also it would be useful if you are able to share a project export (prior to syncing) and we can take a look here.
Basically, it's a Red material with WAV audio files recorded on the external recorder. Selecting all video and audio files in the Media pool and using either Auto-Sync audio based on TC or the one with the append tracks causes Resolve to stop responding with beach ball and audio sync never happens. As I said, rolling it back to 11.1.1 works fine. The project is 23.98.