500 error when creating an issue

Hi, I have gitea 1.15.2 running. With this version, in every repository when I try to create an issue, it gives me 500 error. Any clue?

Update: in the log there is following error:

2021/09/14 16:15:30 …rs/web/repo/issue.go:980:NewIssuePost() [E] NewIssue: generate issue index failed: pq: syntax error at or near “ON”