I just closed on my house 2 weeks ago and I decided to refinish my almost 80 year old floors in the lower level myself. Clearly I’m no professional- so go easy on me...

I have red oak floors that were finished with oil based poly probably a million years ago, they were very orange by the time I got here. I sanded the floors about 2 weeks ago, stained them last weekend with an oil based stain, and had always planned on using a water based finish to avoid my lighter color ambering. I put on 2 coats of water based finish yesterday. After the first coat I came back and there was this weird spot near my front door. Upon closer inspection, it looked crusty and sure enough, it flaked right off. The rest of the floor looks great. This spot literally came right off with rubbing lightly rubbing. I got off all of the crustiness and tried again. I coated just those small spots, let them dry, and then applied my 2nd coat to the floor. I just got to the house and the same thing happened in that spot. Again I scraped it off then sanded. I applied another light coat of finish and it has done it again. I have no idea what is causing it and I'm panicking.

Any ideas?? Photo linked below.
https://photos.app.goo.gl/6DusJagx47oJTVoB8

(I also posted this in the "Floor refinishing" forum, hope you don't mind)