I reported this same problem last week in the POST-PRODUCTION forum:
http://duc.avid.com/showthread.php?t=405570
The only way we're able to make start times what they're supposed to be is open the file with Sound Device's app., WaveAgent.
https://www.sounddevices.com/product/wave-agent/ It's free and allows you to edit the start time.
BTW, if you try to re-import the BWF and spot it in your timeline, you will see USER TIME as the correct TC, but that listed START TIME is incorrect.
We've been working this way for 10+ years and just recently started having this problem. Using Mac OS High Sierra and Pro Tools 2019.6. Reverted back to 2019.5 and deleted all prefs, which changed nothing. Problem still exists.