Getting a 500 error when trying to access two repositories

[LeeR]

We have been running a self-hosted bitbucket server for several years.   Presently we are running version 6.10.0 on Ubuntu 18.04 64-bit server.  Last week, two of our repositories mysteriously started returning the following error when attempting to access them:

'/usr/bin/git cat-file -t refs/heads/master:' exited with code 128 saying: warning: ignoring broken ref refs/heads/master. fatal: Not a valid object name refs/heads/master:

I ended up recreating new repos from a local copy of each so that our team could continue development.   However, I am unable to delete these repositories via the Bitbucket web interface. 

How can I remove these repositories from the list?

Thanks!