Matomo strange behavior - IP lock by provider

I have a really strange problem. A matomo installation worked well for several month. Than we recognized, that for the last three days there were no visits reported. I thought: “perhaps the update to a newer version will help” - tried it. First attempt didn’t work, second attempt worked (just the update, not the newly report of visitors).
After that, there were some file-leftovers which were recommended to delete. Did it.
Than Matomo told me, that the Database has to be changed to to utf8mb4 chaset. I activated the background task, looked after a few hours but nothing happened. Tracking was green.
Since then (I don’t know the exact “time”) I have the following problem. If I lock in, I see everything. But if I go to the admin section and click something in the adminemenu, my IP get locked immediately by my provider, because of several failed Login attempts, they told me (but I didn’t login).
I have changed passwords, and I made a new installation but with the old database. Same problem.
Is somebody here, who has an idea what this can be? I’m afraid of a hack, but on the otherhand everything started with this update and database problem. Before that, I could navigate in Matomo while searching for the initial problem, that the visitors weren’t reported. Can there an activity in the background which causes this issues? The website I am tracking is made with WordPress.
Sorry, for this long thread, but I try to give all information I have. Has anybody an idea what can cause this problems and how I can solve them? Right now I can’t do anything in matomo because the IP is locked before I can do any admin work.
Thanks in advance

Hi, after a perfectly new installation with a new database. The same problem occured. I figured out, that there must be a problem with the fail2ban firewall of my provider. They say, that they need to know from matamo what the issue is, and what they have to change in their configurations. Can anyone help with this? Or where I can get the information.