The fix for this issue is included in 9.1R8.1 which is released, please refer release notes
and will be included in 9.1R9 tentative Mid October 2020.
PRS-392254 SNMP polling was not returning false PCS Model Number and device type. This is addressed in 9.1R8.1
The following OID can be used to find the required information:
SNMPv2-SMI::enterprises.12532.7.0 = STRING: "9.1R4 (build 4763)
SNMPv2-SMI::enterprises.12532.6.0 = STRING: "Pulse Connect Secure,PSA-5000