I was supposed to climb to the top of the mountain then swim in the caverns to complete this quest. About halfway up the mountain I saw that the instruction on the screen said to go to the caves which I did. After completing this I had to leave the caverns and return to the quest giver who complemented me on completing it. I later watched a video and discovered that I had a long way to go still to the mountain top yet the quest completed without me doing so.

Had you already climbed to the top and recovered the "crimson" scarf?

You only have to do this once, and "earlier" counts.

No. Never been to the top, but quest shown as successfully completed.

Sounds like a bug, please send a full description (and a save file from before the attempt if you have one) to http://en.cdprojektred.com/contact-support/

Best way to get it fixed.

Probably got broken while closing the XP exploit.

In the meanwhile, continue to the top, collect the scarf (in case it is needed for completion still) and the place of power. There is a signpost for fast travel (or you can go down the short/fast way) once you have done the run once.

I will see if I can find the location again then climb. This happened a few levels back.

OK. I climbed the mountain to the top this time where there is a place of power and a fast travel post but found no
item of clothing. In the quests completed list this quest is shown with each objective completed, marked with a tick in green.
Strange indeed!!

It should be high on the pillar in the centre of the platform at the place of power. Loot this pillar to collect the scarf.

If you'd never climbed the path, the scarf should still be there, and the quest not moved on. The situation seems un-normal and not as intended.