Driving Focus keep turning itself OFF after manual activation

Hey there!

I searched through these forums to find mentions of similar issues, but could only find people having problems with Driving Focus automatically turning itself on when it shouldn't. My problem is the opposite.

I ride a motorcycle and would like to use Driving Focus while on the road, since I absolutely cannot respond to calls or messages during that time. So, I turn it on manually before I head out.

Yesterday, however, I noticed when I stopped that Driving Focus had turned itself back off while I was driving. So, I activated it again manually before I got back on the road ... only to notice on the next stop that it was off again. This happened about four times during my ride – or, more importantly, every time (usually noticed after about 30-60 minutes, but might have happened sooner).

I checked the Focus settings, but they are all pretty standard (activation is set to manual or via CarPlay; everything else is default):

The only other thing I could think of is that I'm also wearing an Apple Watch while riding. But that just sits untouched under the cuff of my coat and it's really difficult to accidentally enable or disable a Focus on Watch, anyway. So, I doubt that that's it.

Would be interested in hearing any ideas as to why this might be happening, or even just from other people who've experienced this.