Answering @Nadahar‘s specific questions/points:
I actually wasn’t aware that this is expected behavior. Indeed when I saw this it may very well have been related (sometimes? always?) to situations after the cache was cleared automatically (or even by me?). A consoling console message would have been helpful to prevent near heart attacks now and then. 
Could well be. If I encounter this again (with the EnOcean binding or elsewhere), I’ll swear less and instead watch out more closely for log messages, also a bit further back in time. The problem with this one is that I don’t have very many EnOcean devices, and they don’t have a heartbeat or so, so it usually takes a while until I even notice that they have fallen silent.
It was discussed before in the forum, in 2022:
And again in 2024:
Seems to have happened to quite a few people. The last post in the older thread says something about overriding icons in the sitemap file (which indeed I do occasionally), but I don’t really understand why doing so should be a problem, because being able to do that is an intended feature. So after reading that thread back then, I just shrugged it off as yet another case of “no, certainly that’s not what it’s meant to be, but if nobody cares about it being buggy, it doesn’t keep me from doing what I want to do, so I won’t waste energy either”, and accepting that this stuff will likely fill my logs forever.
Yes, there have been forum posts, and also an issue: [homeconnect] Handler was already disposed · Issue #17037 · openhab/openhab-addons · GitHub . It was closed, though, after someone else reported that some other problem that was discussed on the side had vanished.
Again, important disclaimer: I know why didn’t get help with that - namely because I didn’t ask for help. It’s just examples for why I grew tired of even asking for help, and why in the initial post in this thread I said (not literally, but basically) that OH oftentimes feels like a squeaking, rattling old car, which mostly does it’s job, but it doesn’t really feel like it’ll do that for much longer (subjective, colorfully described impression, not objective truth).