Hi!
Thank you very much for all the details, I managed to find the problem. I force-enabled error reporting, and turns out, that the issue was with an object to string casting function. Basically, when the indexing was triggered during the post saving process, the plugin tried to get the contents of the selected ‘_fb_builder_data’ custom field. However, that field contains some objects, that cannot be properly converted into simple strings, and that caused an error.
I made a tiny modification to one of the search plugin files, that checks, if the given thing is an object, and if so, then skips it. Now it should work as expected.
I will make sure to inlcude this fix in the upcoming release, so you won’t have to worry about it.