2016 CRV brake pedal occasionally won't depress to start the car

I’ve read a little about this, but there does not seem to be a viable solution (that I’ve found). What happens is, you get in the car, push on the brake (but it won’t go down), try to push the start button, and of course it won’t start because the brake is not depressed.

This happened to my mom today (and has happened once before). She was at the grocery store and couldn’t start the car to come home.

I understand that this is a vacuum “boost” system issue. You press the brake and the boost doesn’t kick in, so the brake is difficult/impossible to push.

Typical responses online are that they suspect that the brake was depressed a few times after the car was turned off and it drained the vacuum system. This is not the case however. My mom tried a few times and it wouldn’t depress. She got out of the car and called home. She got back in the car again and tried again. This time, the brake depressed as it should and the car started. So the vacuum system was not drained and we don’t know what was causing the brake to be stiff the first few times…

Numerous others in forums online describe similar situations. A number have also claimed they took their car to the dealer. The mechanic could not reproduce the issue and send them home without doing anything.

So what I’d like, is to figure out a reliable way to get it to start the first time. Perhaps there’s a work-around or a way to get the boost system to engage? Is there anything that can prevent the boost system from engaging? Could a low key battery cause the boost to not engage?

Unfortunately, it seems like a difficult issue to fix since it can’t be reproduced on demand.