Wordpress Site not Displaying Correctly (Stripped back version) and Unison Plug-in Issue

I have a Wordpress Site with courses/classes for ukulele. The site has been inactive for quite a while, and I am trying to get it back up and running with some changes. I have a critical error on my site: An active PHP session was detected - A PHP session was created by a session_start() function call. This interferes with REST API and loopback requests. The session should be closed by session_write_close() before making any HTTP requests. By deactivating my plugins one-by-one, I have isolated the issue to the Unyson plugin. I believe this needs resolving manually, could you do this? The site is also not displaying as it used to - it's a very stripped-back version. I was unable to access my site as administrator. Support at Namecheap (where I have hosting) identified the Learndash plugin was causing the issue, and I have been able to access now, update and address some of the critical errors. (I am looking at using an alternate plugin now with all of the Learndash company changes - I'm thinking of using Tutor LMS). I had thought that with renewing my Learndash subscription and getting support from Learndash, the display issue would be resolved, but maybe I'm wrong? Could you advise what is causing this issue and the best way forward? Could you also provide an estimate of how long this job could take.