"Fortinet" type device which had additional .1 in BGP MIB as mentioned below resulting in SNMP_EXP_NOSUCHINSTANCE
.1.3.6.1.2.1.15.3.1.2.#.#.#.#.1 INTEGER-32 6
All supported Smarts release
The polling index does have an additional .1 in BGP MIB, Which is the cause for the PeerState query returning as NoSuchInstance from the device.
Fix is delivered as part of Smarts release 25.4.5.