It really sounds like the problem is with the lock ring, problem with a quick link or frozen link, or a stretched chain/worn out cogs. When I look at the movement of the chain, it looks like it is getting hung up on the either the cogs or the pulley wheels. Is the chain properly installed through the derailleur? What did you do to the drive train before putting it back together? Being that you state it is friction shifting, I believe that means the problem is more likely with the chain and the cogs.Maybe you should take it back to who worked on it.