iPhone has started reporting my AirTags left behind

On 23rd April I got a message on my iPhone 16 and Apple watch 7 that I'd left my keys (with an AirTag) behind. Find My reported them to be at the last place I'd visited and I raced back there but couldn't find them. A thorough search revealed they were still on my person! I fell for this without first checking because, until this time, in several years of AirTag use, I'd never had a false positive.

However, since that day I've received more false alarms—sometimes more than one a day—for AirTags that are with me, and it has happened with several AirTags (including one with a brand new battery).

Something has changed; either the behaviour of the Find My network has changed, or the behaviour of my iPhone has changed. Is there a way to test the Bluetooth?

Does anyone have any suggestions?