Poor PFA fixation often causes trouble in antibody staining. Folded cells, poorly preserved cytoskeleton… These artifacts appear when the stock of PFA gets older and degrades. Buying ready made PFA solutions, most of which contain 10-15% of methanol, can also lead to low labelling with some antibodies.
Glyoxal seems to be a good alternative. It had the added advantage that it is less toxic.
Check this article to know more. 🙂