This could be solved by not letting the familiar hide as a bonus action. While the process might sound tedious, it's pretty easy once you get the hang of it and I was even able to solo the four level four gnolls outside the blighted village with JUST the familiar.
That should be solved by just making the AI search for it. I've managed same trick *in combat* (just need few corners and dark room) so not like fixing familiars will remove the exploit.
