There are many threads on this topic. It’s a pretty well known fact that the openhab implementation of homekit is out of date with several issues.
A workaround for your issue that I used before replacing built in homekit was to stop openhab - then edit items - then restart. It cleared my settings less often.
Here’s a recent question about exactly your issue:
That being said, homekit in openhab still leaves a lot to be desired at this point. Many of us on the forums have started using nodered - which has been fantastic in my setup. Here’s a whole tutorial I put together about how I’ve replaced homekit (note a few posts down I’ve linked to other people doing similar tutorials):
