Please, take a look to the attached GIF.

Resetting Bar Settings should only reset actual bar settings (F5 on any bar -> tempo changes, beat changes, style changes, etc...), and not Bar-Based Section Letters.

This one looks not very difficult to fix.

Nice clear video. Cerio, to help diagnose this, is it BIAB 2019, which build, and 64-bit only?

Thanks, yes same problem with 2019 32/64b.

Does "Reset all bars" also deletes Bar-Based section letters in your system?

Just tried it, and yes, it did.

I wonder if it's related to the fact the Help on this is reversed (which I've reported). Click the Help button and you'll see about Reset Bar and Reset All Bars. But that makes me think this behavior is intended.

Not sure if I'm understanding you correctly, Matt. Anyway, I dont think this behavior is intended: Bar-Based Section Letters is not under "Bar Settings Change" (F5) window, there's no reference to that feature from there:
https://www.pgmusic.com/manuals/bbw2018full/chapter6.htm#_Settings_for_Current_Bar

Additionally, if you assign a section letter to any bar, it won't appear any red line indicating bar changes on that bar, and nothing will appear when you click on "Print summary".