Oh my gosh, this must be beyond frustrating. I’m pretty stumped myself. I cannot think of a reason the cells would survive with no f-actin. But…maybe something in your solutions is causing the actin to depolymerize before it’s fixed? Have you tried the age old replace-all-solutions-from-start-to-finish?
I never had troubles following the Ted Salmon lab IF protocol. If you aren’t working with microtubules you can eliminate the glutaraldehyde in the fix and skip the sodium borohydride quenching step. I can’t remember if the Hepes is for the MTs or the actin (it’s been many years)… Good luck! We’re rooting for you!