Yesterday I found one of the issues not being seen in search results and unreachable even by direct link, that I found in my mail.
I'm the only administrator in our cloud based Jira software. In the permission scheme linked to the issue I am the only one who has the "delete issue" permission.
At first I was suspected to delete it by accident, but then I asked all the employees who received notifications of this issue change to send me all notifications that they have, and there was no notification of deletion among them.
At the moment, it is not entirely clear to me what happened to the issue and how to see it in Jira again.