Derived Tag ExpressionEval Error

I am using ignition 8.0.6 and have a udt opc tag of document type and using derived tag to extract individual variables, the problem is that at random times i get an error Expression Eval on all variables of the OPC UDT, restarting the tag provider , or simply disabling and enabling the derived tag will solve the issue. Is it a bug or i am missing a configuration.

try surrounding it with coalesce(jsonGet({source},"Stat"),False)

Has there been any development on this problem ?? our ignition (8.0.6) seems to have the same problem and is only cleared once the tag is restarted.