Does litespeed cache cause it?
I don’t think caching is the problem here, but have you tried to delete the cache before adding a page?
If that doesn’t work, please visit the site you want to add and append the following parameter to the URL: ?wpso=show_qs
.
This will output the current WordPress query string to the screen or “global” if you are on the frontpage of your site. If you see a query string, it should be possible to add this site in the backend.
It’s also possible that any other plugin is the cause of this incompatibility. You can check this if you deactivate all your plugins one by one and test it again. If it’s the case, that an other plugin is the reason, then i maybe could identify the issue.
Best regards