There may be a time that you or your visitors will try to look at your online resume, portfolio or blog and during the visit, will will incur a 500 Read Timeout.
Why did this happen? Well, Apache most likely has crashed and when Plesk tried to restart it, the older sockets were still open.
So what can you do about it? If you have ROOT access, you should log in and kill off the old processes then restart Apache clean. Otherwise, contact the hosting provider and let them do it for you.
My hosting provider, Sipylus, occasionally did this for me on Plesk but since they moved me to cPanel, it does not happen anymore.