Lol, I mentioned in another post where sometimes a lot of especially FMQ issues can be solved with a good bobbin case cleaning.
Especially when it is one of those "but everything was fine yesterday" type of things.
I've been having problems with the thread sensor in my Bernina... finally a big piece of black thread was hanging out of the middle of the machine (which had been threaded with white thread for about a week now), and I pulled it out and things seem better now -- guess it really was having an issue even when I couldn't see anything.
I should go do some sewing, I left Bernie on over night because it's wanting particular settings on my thread right now. Usually I don't have to do much adjusting and can use the defaults (other than bringing down the stitch size) but for the last couple of days I have to make two adjustments (which then have to be redone if I turn the machine off).