Running Cron Event Error

I have the issue that I cannot start or stop a cron event anymore.

At the place where the “Start Cron” or “Stop Cron” button is displayed normally I see a red warning called “Running Cron Event” now.

I think this happened because I accidentally changed the filter by text while the cron was running.

How can I resolve this issue? I already deinstalled both plugins and reinstalled them again via FTP. I also deleted my site cache and server cache.

Thanks in advance for your help!