Hi Backlog Enterprise users,
Recently, we found a bug in version 1.11.1 that prevents users from editing and deleting comments on the Git pull request page.
Our team is working hard to fix this bug, and we apologize for the inconvenience.
We plan to release a new version for Backlog Enterprise with the bug fix in early March, and we will provide an update again when the latest version is ready.
Thank you in advance for your patience. 
Update (5th March 2021):
This bug has been fixed in Backlog Enterprise v1.11.2. Please see the v1.11.2 release notes here.