What does this mean? " [**INVALID PROPERTY NAME**"

FG-800C Firewall logs:
What has caused these invalid messages ?

2018-03-31T03:52:31.637611+05:30 wifi-security-server1 - [**INVALID PROPERTY NAME** 

2018-03-31T03:52:31.637611+05:30 wifi-security-server1 - [**INVALID PROPERTY NAME**