Have you had this problem?
Several months ago I bought an inexpensive Brother machine to replace my dying old Pfaff. It took me a while to like the new one at all, but it turned out the upper tension inside the machine is off, so compensating for that helped. The only problem I cannot seem to get over is the bobbin take-up.
A technician at my LQS showed me what the bobbin area should look like, how the thread end should cross over the inserted bobbin and then come up thru the plate. (Please forgive if these are not the right words.) When I need to insert a new bobbin I often have to take it back out and try over and over again, sometimes a dozen times, before it [the thread end] stays in the right place long enough to sew. And then it sometimes slips "out" in the middle of a seam, at which point it begins that looping nonsense on the underside.
Long, long story to this point, but the question is: Have you had this problem, and have you found a "cure"?