I've seen cases in which downgrading to older 25.x releases helps with stability on the older AP's. It's often case by case based on config and usage.
The last case I see on this opened by you was Dec 2020. Perhaps open a new case online and request a downgrade to 25.14 to test stability. You could have Support downgrade just a single AP (or however many you want) to the older release so you can contain the testing to an area before downgrading all AP's.
Ryan If you found this post helpful, please give it
Kudos. If my answer solves your problem please click
Accept as Solution so others can benefit from it.