While git fsck --full was executed as described in BSERV-8524 from other hand Stash still working.

Caused by: org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.atlassian.stash.internal.pull.InternalPullRequest#104916]

This force to_hash field in database for table sta_pull_request rolled back to old commit. But in target branch commit was successful fetched. After what to one PR can't be merged in this branch, because old to_hash point to outdated commit, and HEAD of branch is above any to_hash.

So, after such crash we need perform manually update sta_pul_requests set to_hash for any pr_state == 0 PR to actual last commit in each branch to fix that.