It was me, someone on forums advised me to stop trying and w8 for the OE event to finish. After the event, the knife went to +7 pretty quick. Might have been a coincidence, but I doubt it, since I applied this strategy to other characters later on and it worked.
This month however, I was doing this quest for 2 alts with the free option added in fafurion and failed soooo many times, I think I have lost about 40min per character to finally get a +7 knife.