Lars N. proposes to do experience…. buy or borrow HomePod mini with the option to return and pair the tedee with HomePod again and check … then you will eliminate everything possible for 100%
I have checked with a HomePod mini that I borrowed. Same results
Lars N. okay ! what IOS do you use? 15.0? 15.01? I use such a system Iphone X and Ipad 8th generation If it is not the fault of the software, it remains to replace the Tedee lock You have already checked everything that could have caused the lock to malfunction. new homepod + lock tedee showed a bug This is what it looks like 
Lars I moved the conversation to separate thread: HomeKit comunication issue (Lars) : Tedee (freshdesk.com)