This has started appearing in my event log. I haven't (to my knowledge!) changed anything recently.
uniFiAP Error in Line 6746 has error=No JSON object could be decoded,receiving DICTs for 192.168.1.5; check unifi logfile; if this happens to often increase DICT timeout
uniFiAP Error ... APdict 192.168.1.5 error in the JSON data, #of bytes:95
uniFiAP Error ... JSON=Study-BZ.v4.0.80# mca-dump | sed -e 's/^ *//' Study-BZ.v4.0.80# xxxThisIsTheEndTokenxxx1...
... udy-BZ.v4.0.80# xxxThisIsTheEndTokenxxx1
uniFiAP Error APdict 192.168.1.5 forcing restart of msg after due to error count in json