If this is a connection issue: suggest that you take the TRV off the rad and move it near to the internet dongle. Check the battery voltages or swap for fresh batteries. If it’s still offline, that sounds like a faulty TRV.
If it works near the internet dongle, swap the TRV for one that is nearest the dongle. To recalibrate the TRV on the rad valves, take the batteries out for a minute before reinserting. If the off-line fault stays on the original rad with the swapped TRV, it suggests a wireless range issue.
For 24 TRVs: we swapped one trv that kept going off-line as it ate batteries, one trv occasionally drops connection, and one rad has the original manual trv as it is too far from the dongle.