Did you recently upgrade your php version? Someone in this thread:
https://vborg.vbsupport.ru/showthrea...80#post2297380 was having a problem that was related to the pcre.backtrack_limit setting. They weren't having the same problem as you (and I don't really understand what the setting does), but you might want to try commenting out that line in init.php and see if it works for you.