I have this problem with my MM Shamu on my WBBB 1.7DL sometimes. For me, the #1 culprit is my hammock is slung up too tight. When I have my ridgeline with the proper amount of slack my UQ stays put, if it's just a bit too tight so is the UQ, which is pretty narrow for my broad showlders, and commonly slips off my left shoulder.
I thought about getting something to clip it in place, but after much trial and error, and the help of my GF, I was able to find a sweet spot and figure out the root cause to my problem.
"The more laws that are written, the more criminals are produced." - "The more laws and order are made prominent, the more thieves and robbers there will be." - Lao Tze
"Good people do not need laws to tell them to act responsibly, while bad people will find a way around the laws." -Plato
Hammock Forums is my social network.