@kompala Naveen’s fix matches your config. In the account schema you posted, groups is linked to the group schema but has "isManaged": false. The Connector Specification File docs define managed as “Whether the entitlements are manageable through SHF (true) or read-only (false)”. A read-only entitlement fits the "attribute": null you are seeing.
If attribute is still null after you set Managed and aggregate entitlements again, also add this to the same groups attribute:
"schemaObjectType": "group"
Right now groups points to the group schema only through the schema reference. In the thread Harish linked, the cproblem was still the same until schemaObjectType was added (post #20).
On where to get the logs, SailPoint added a log download for SaaS connectors last week (announcement). It is under Admin > Sources > your source > Additional Settings > Administrator Settings and covers about the last 24 hours. You can turn on debug logging there and download again. It reached sandbox tenants on September 21 and reaches production on September 30. If not, you can reach out to sailpoint support.