After selling 1000 sweat and making more than 20 PEDs for it, I received the following message:
"Your attunement with this universe is too great, and your ability to gather Vibrant Sweat is lost."
I've then looked into my skill range and had level 67 as a Sweat Gatherer.
I found out later, that this was a provisional situation. I was able to gather sweat later on in the game.