I have tried deactivating all plugins but the issue persists. Switching back to default theme doesn’t seem to help either. Tried resetting the plugins folder as well, no effect. Doing a re-upload of wp-admin and wp-includes now.
My current memory limit is 128M based on my .htaccess file. Is that enough?
It is weird as the problem seems to be with only posts, I can edit pages and comments with no problems.