PHP 503 errors are generally PHP crash errors. This is not a LiteSpeed Web Server error. However, for convenience, LSWS provides a feature to auto-fix a 503 error by restarting LSWS. Enabling this feature has advantages and disadvantages.
When random PHP 503 errors happen, this feature can keep the affected domain alive by auto fixing the errors. However, if the PHP 503 errors happen frequently, across the majority of accounts on a server, LSWS will end up being restarted often. This can lead to a stability issue. In this latter case, fixing the 503 error permanently should be your ultimate goal. You will need to determine which situation you are experiencing, to enable or disable the Autofix 503 feature accordingly.
To turn off the Autofix 503 feature, you can log into LSWS Admin and change it.
We do provide a comprehensive guide for you to troubleshoot 503 errors yourself, including checking logs, disabling the opcode cache for PHP, increasing PHP memory, changing PHP versions, disabling unsafe extensions, checking disk space, checking LVE memory limits, checking LVE process limits, etc. We use the same guide internally to troubleshoot 503 errors.