When OpenPilot is engaged on my car, it uses OP lat guidance and the stock ACC/SCC system for longitude.

When engaged, if I hit the "pause" button on my steering wheel, the system is paused normally.
If I tap the brake pedal, the system is paused, but I also regularly (but not 100% of the time!) get an error message on the dash and audible alert from the car (not the Comma 3X): Smart cruise control conditions not met.

I think (but haven't totally narrowed it down) that it might be related to speed - above 26ish miles an hour, it basically always happens, below, it doesn't seem to happen.

This drive has the issue happening several times, and several times where it didn't happen. I also used the pause button a few times.
https://connect.comma.ai/0ec5742cd5c8d623/00000000--6e1ce11393

Let me know if I can provide more information. Happy to help troubleshoot.