I have the HQ fusion, and had a lot of tension problem until I discovered I had 5 bobbins that did not spin as freely in the bobbin case as they should have. I use a Towa gauge to set my bobbin tension and keep it around 180 no matter what thread I use. And this does mean adjusting for every thread change.
I added the digital readout for my upper tension too, and now have very little tension issues. The only thread I've had problems with is Connecting Thread Essential Poly - as it likes to jump out from under the spring on the bobbin case. So far it's the only thread I've had that has done that, at least when it does, it's real easy to remove.
I sometimes have to change the thread path as some cottons like to loop more than others, and sometimes it will pull a loop into the tension disk and then I'll get a blip of thread underneath. And once in a great while it will pop the thread right out of the tension disks. I don't go as fast with cotton thread and that seems to help.
So far, the only thread my Fusion really does not like is the Connecting Threads cotton. Though I have not tried them after getting all the other tension issued figured out.
I have found some variegated thread is not constant in diameter, I've read it's due to the dies used, but don't know that for sure.