Could be something else, but the error is attributed to APR.

9/18 19:43:10.473 An action was blocked because of taint from AnnoyingPopupRemover - Search()
9/18 19:43:10.473 Interface\AddOns\Blizzard_LookingForGroupUI\Blizzard_LFGBrowse.lua:225 LFGBrowse_DoSearch()
9/18 19:43:10.473 Interface\AddOns\Blizzard_LookingForGroupUI\Blizzard_LFGBrowse.lua:178 LFGBrowseFrame:SearchActiveEntry()
9/18 19:43:10.473 Interface\AddOns\Blizzard_LookingForGroupUI\Blizzard_LFGParentFrame.lua:92 LFGParentFrame_SearchActiveEntry()
9/18 19:43:10.473 Interface\AddOns\Blizzard_LookingForGroupUI\Blizzard_LFGListing.lua:67

This is almost certainly not APR related. It's due to some other addon that shares a common library with APR. The other addon interacts in some way with the quest window or the LFG window, and that's causing the taint. If you try the same actions again with only APR enabled, it won't taint.

If you can give me a complete list of addons you have running, I can double check to be sure, but I'm 99% convinced this isn't an APR issue.

Yeah figured. (=

Elv has been buggy AF since updating to their "unified all WoW" version. Guessing it's Elv. Not likely anything you can do. Thanks mate!