Lift bucket in tub won't go down enough
These get blocked by hair and soap buildup all the time there was probably some scum on it when you removed it (now matter how clean the tub is).
An old wire coat hanger can be used to scrape around and pull the remaining soap/hair out. Or the purchase of a small hand auger and slide it in and rotate to clean.
I really don’t like drain cleaners in these cases but if you can just put a little down and let it sit it may dissolve the blockage once it will seal  let a small amount sit in there and rinse it down.
But if using drain cleaner they sometimes discolor the plumbing / tub so I never over fill the pipe if I do use cleaner.