Had the same issue – the root cause was a “bad” parameter from the LiteSpeed point of view. Correct the field value and it will fix.
More context: if you look closely to the returned page, you can see that in the footer is it written that the page was returned by LiteSpeed – this may mean that it found something that bothered. Please check the request parameters that are sent to backend and identify if there is something strange.
For example, in my case, the issue was when calling /wp-admin/user-edit.php for updating a user password. This not made sense because it failed for only one specific user. I have checked the parameters that were sent and name was having its value something like “[email protected]” – so in a name field was samed an email value. I have changed the user name field to be a normal name value and the problem vanished.
For more reading on this: https://forum.ait-pro.com/forums/topic/bbpress-bulk-user-edit-403-error-user-edit-php-403-error/