I've seen   debris  ( degrading  o-ring  material)   pack  against  the    tip  on the   return  hose..   I have a   field cultivator  that  did  it   when   trying to    lift  on the end rows...  

Both lines  would  jump  with pressure,   so   I knew  oil  was making a  full  circle,   it  just  couldn't  make it  past the  tip.