Does #12 still have the problem as #11 with deleted renders re-appearing ? If so, the trash-collector needs another kick.

Also, FBX imports (*) whose rigs come apart into many sub-rigs seem to choke both the hierarchy and material / texture handlers.

Um, a bit retro, but equivalent would be how 'bubble sorts' clog beyond a certain size of data-set...

*)  HiGuys920 over at DA seems to have knack of rigging FBX figures to 'play nice' with Poser. Single rig, 100% original scale. As it should. 

So far, he's 'Three from Three', with a dozen more to try. I've asked him to do a tutorial on work-flow...