This is a common problem with the varios - if you use them a lot then expand and contract them frequently to keep them free running.
It happened with my 2005, 2010 and my 2013 varios. I got my dealer to fix mine last year but they are stiffening up again even with a lot of use. The plastic on the lid section seems to bow upwards when the pannier is contracted and they jam in the corners - can't quite work out why this happen but when it gets too bad again I will ask my dealer to sort it out
I bought a pair used Varios on fleabay and they were seized. I completely dismantled the gear mechanisms, cleaned and lubricated everything, but they still didn't vario at all easily. I use silicon spray as a lubricant. I don't know of a YouTube demo but if you do dismantle take care and photos, and make notes. It's easy to reassemble so that the sides are out of sync.