I dunno for sure if it would help, but did you try using a high powered pressure washer? It might be able to tear up the paint that's left. If you don't want to paint it again with normal paint you could look for this stuff thats sort of like "non-skid" for flight decks of navy ships...but it's not as coarse. It's kinda like soft stucco. You just roll it on like paint. I dunno just giving you some ideas in case it doesn't pan out.

i just stripped 25 years worth of paint off an old victorian front porch with a product called peel away its a paint remover that you apply then cover with a wax like paper it removed all the paint and stain the only thing you have to be careful with is washing the deck after to make sure all thestripper(lye) is removed it worked well for me

Good suggestion and if the peelaway doesn't work I would only re-strip the floor and see how that goes. I know more hard work.