When did this happen? Recently the board was getting overwhelmed with processing and yesterday between 9 and 10 they moved the board to a new instance that could accommodate the load. You should see far less of these messages from now on.
Perhaps it could be that an iOS or Safari update is needed for your phone. What version of iOS do you have? I’m not seeing it on my 256 GB iPhone SE 2 with iOS 15.4, and never saw it on any of the earlier iOS versions or my iPhone 7, but it may be that some platform updates on the Hubitat forum software now expect more recent json processing. Have you tried a different browser (Firefox Focus or Firefox)? All the other iOS browsers use the same underlying Safari WebKit.