If you add

Related: https://pagure.io/project1/issue/NN

to a commit message in project2, ticket NN then references an non-existing commit, because it assumes the commit is in project1 instead of in project2.

Example:
https://pagure.io/fedora-workstation/issue/88#comment-556271
https://pagure.io/fedora-comps/pull-request/373

The comment in ticket 88:

Commit 35d36cf9 relates to this ticket

links to https://pagure.io/fedora-workstation/c/35d36cf9 which is 404 because it is in a wrong project. The commit was pushed to fedora-comps, and the link should instead be https://pagure.io/fedora-comps/c/35d36cf9 .