I am battling the same/almost same stuff. Started out as little white slimy hairy stuff on the inside of the glass.
Think it was a hitchhiker on the piece of wood I put in the tank. Removed the wood. Daily water changes didn't help. several tear downs not helping either. would come back within hours.
Heavy dose of peroxide seems to be what's made the largest difference and also sterilizing the filter media.
murdered all the guppy grass, melted some of my crypt but it seems to be going away. Tank is staying mostly clean of it for 4 days straight now. It was even in the filter media on my HOB. I wouldn't be surprised if it's in yours also.
Mine turned into a much larger issue (assuming it's related) of what looks like Periphyton. I posted about it. Took over the whole tank. Could also potentially be a type of slime mold. my own research pointed me in that direction but I could be wrong.
So long story short. I'm doing black outs on the plants isolated since it's on them til they come clean. and moving them to another tank and then just restarting the tank. I don't have fish in the tank so I'm being aggressive with it. I don't have this problem with my other tanks at all. Could also growing pains of my tank maturing too. There are other people that appeared to have the same issue but I couldn't find a solution.
Your issue could resolve itself with time though.