I know this feeling. I’m not a doctor and I can’t offer a thorough explanation. I am prompted to share my experience though in the hope that you find it helpful.

For a long time I was focused on forcing the yawn or otherwise putting effort into it as you described. What I realized was that the missing ingredient was the depth of my breath. My body is trying to relax, initiated a semi-autonomous routine to do that, and I’m interrupting it.

When I’m too tense I have trouble yawning. If that’s happening the only sure way I’ve found to satisfy the yawn is to drop my shoulders, breathe from my stomach first, and let the yawn take over. Sometimes the jaw still ends up pushing open quite wide. Sometimes not. The key is that I’m not trying to control it either way.

Now it feels as odd to force my own yawn as it does to overthink my own breathing. The only viable solution seems to be giving up on control over it and letting my body go on autopilot instead.