since you are using plesk, plesk PHPs are recommended. PHP compiling on LSWS admin console is for LSWS native mode, not for plesk control panel at all.
Install and configure like the following, Make sure apache and LSWS use the same php.
Please follow the following wiki to get your PHP configuration right.
https://www.litespeedtech.com/support/wiki/doku.php/litespeed_wiki:plesk
Most of the issues looks like PHP setting issues, Please switch between apache and LSWS to see if your apache has the same issue or not, if apache has the same issue, you will need to adjust some setting from php.ini used by plesk.
If it doesn't happen to apache and only happen to LSWS, you can log a ticket with us with tmp root ssh login and detailed steps to reproduce your issue, then we can take a futher look.