Yep, it filters by a post type which contains from 35-40k posts. The “Filter by Post Type” field has a single entry. The Filters field has Search checked. Return Format is Post ID. The rest should be defaults.
I know the number of posts is the reason as I’ve run into countless other performance issues I’ve managed to work around or resolve. It didn’t have this issue before the AJAX was implemented therefore maybe an option to not use the AJAX or somehow automatically disabling AJAX if there are more than a certain number of posts for that particular post type could prevent the slowness and crashing.
I’m personally fine with it the way it is now that I’m home and can work from my desktop but I imagine people with less powerful servers and clients would have much more of an issue with even many less posts than I have.
Extra testing results: On my desktop in Opera the page takes about 8-10 seconds to load. On a Galaxy Note 4 in the Android Internet app it crashed. In Android Chrome it loaded eventually but very slowly. Additionally, hovering over the field when editing the field group is a bit slow as well as opening the field to edit it.
