My rear avid juicy 5 seems to be semi seized? After a week left it seems to get a bit locked up if I then wheel it back and forth and pull lever a bit it seems to free up enough to ride. But the bitting point is immediate, no modulation. Now would love to put this down to expert bleeding but my front is like treading on a sponge cake. There is obviouisly soemthing wrong but any ideas? Would replacing pistons help?

Also, when i change pads the the pistons dont seem to return fully?