Fortimanager Error when edit variable mapping "Failed to add per-device mapping to FMG variable"

[Nour_Alkonsol]

Hello 
we have Fortimanager giving the Error message appearing every time trying to edit variable mapping.
"Failed to add per-device mapping to FMG variable"

we tried :
diagnose dvm check-integrity
diag cdb upgrade check objcfg-integrity
diagnose cdb check policy-packages
diagnose pm2 check-integrity all
diag cdb upgrade check reference-integrity
diagnose cdb upgrade check +all
But the above commands, unfortunately, didn't work

Any Advice?
Thanks