SNMP plugin for Fortigate Virtual Domains - the same perfdata displayed

At the first glance I can’t see any issues in your script.
what is the output of the commands?

cmk --debug -nvv --checks fortigate_vdom_mem your_fortigate_name_in_cmk
and
cmk --debug -nvv --checks fortigate_vdom_cpu your_fortigate_name_in_cmk