Modbus binding, problems with silently disconnected items

You’ll have to explain that. Each poll either works or it doesn’t, failure will be reported in your openhab.log.
I don’t know quite what Items going into error looks like, it’s usually the Things that are affected.

Quite a few Modbus-TCP devices can benefit from minor tweaks, like increasing the time between polls, or reducing connect-disconnect rates. For any given device, you have to experiment a bit.

Some background