The manual posts is a bug. Are you able to try the beta above and check?
There is a bit of misunderstanding around fulltext indices and not helped by hosts. While sql queries for these can be heavy on the first load, my plugin has an inbuilt caching mechanism to reduce future loads. My pro version is used on a massive site with negligible impact.
Separately, if there is an edit issue, please do disable the plugin first and see if this goes away. You shouldn’t need 512mb limit for editing posts as the only place the plugin does something is clean up the cache key and save post meta on save. Only reason I see a big issue if you have a bloated meta table and issue with the index.