See here:
in particular the post which mentions MULTI-TRACK AUDIO and says:
Normally issues in Premiere come from people ignoring the DO NOT RECORD TO MP4 warning that pops up whenever it’s selected.
It’s there for a reason .
Premiere hates the mp4 files that OBS creates. Most video editing suites do.
Record to MKV if you need multi-track audio, or FLV if you do not. Then REMUX to MP4 from OBS’ File menu, Remux Recordings. It takes seconds, and Premiere actually works nicely with remuxed mp4 files.