Backup restore issue after upgrade from 7.8 to 8.1.12

After recently upgrading our STG cluster to 8.1.12, our restore job from a v7.8 PRD backup failed. Despite no error messages, the ‘Query running…’ indicator simply spun indefinitely.

Upgrading the PRD cluster to 8.1.12 , and creating backups again, didn’t solve the issue. Observations follow:

  1. in PRD: backup/restore of any dbs (from 8.1.12 or 7.8, local or GCP) without any issues
  2. in STG:
    a. restore: of any dbs (from either 8.1.12 or 7.8, saved in GCP) result in endless “Query running…”
    b. backup: to GCP would miss the BACKUP_COMPLETE file, but status = Succeed
    c. backup: to local would have the BACKUP_COMPLETE file
    d. restore from #c: no issues

I’ve dedicated the entire day to resolving this issue, but I’m still unable to find a solution. My final option, if all else fails, is to rebuild the staging cluster. Any assistance you could provide would be immensely appreciated.