1.24.x Ubuntu, fairly stock. It was working well.
I accidentally added a camera with same IP as another camera and I THINK that triggered infinite load time.
In case someone else runs into this:
I couldn't delete the monitor because when I pull up the ZoneMinder console I get infinite webpage load time.
Shutting down Zoneminder and
Imysqlcheck -u root -p -r --all-databases and all was OK there.
Restarting zoneminder didn't help.
I found I had MANY apache2 processes. Stopping apache2, restarting zoneminder, restarting apache2
gave me a window of enough time to delete the duplicate IP and all is well again.