As per the network capture, this seems to be caused by SNMPv3 Engine's ID
A first option would be to follow the steps described on next technical document to clear the SNMPv3 cache in Spectrumhttps://ca-broadcom.wolkenservicedesk.com/external/article?articleId=139839
If that does not work, another option is:
1. manually create a GnSNMPDev model using new model by type
and give the IP of the device you are trying to model
2. once it is created, manually change the community string to be the correct v3 string (#v3/P:MD5^<authpassword>:DES^<privacypassword>/<userid>).
3. Then right click, and select – Reconfiguration – Reset SNMPv3 Credentials.
If the above steps still doesn't work, you may try destroying the GnSNMPDev model created (destroying the model is supposed to remove the entry from the cache) and try modeling it by ip.