I occasionally have the same problem but mine is on the drivers side seat section, if I work it up and down several times it will go all the way up.
Never had it not go up after several tries, usually only takes a second try.
As you said something metallic is catching, but I have not been able to find out what as of yet. I lubricated the pivot points on the hinges and it seemed to help a little but it still binds sometimes.
Almost seems like some sort of safety lock function on the seat, kind of like when the seat belt straps lockup and you have to release them to pull them out further.
Will be interesting to see if someone chimes in and has the answer to this, I have gotten a lot of helpful info on this site over the years I bet somebody will know the answer.