Maximizer goes through all your familiars to find the best one (two if you have both CoT and BB) familiar, by seeing if they are better than none first, then if they are better than the current best (and/or second best). With -tie it doesn't do tiebreakers, so doesn't think any familiars will help more than none, as none help with +adv. If you don't have any other back items that give +adv, none of those are suggested instead of what you are wearing. The result of these two is keep what you have, but with no familiar.
I guess what I could do is default to current Familiar if removing familiar is suggested, though if the current familiar is worse than none that would produce a bad result. I'm open to suggestions that will always work and not do something bad. This one did indeed maximize adv accurately.