Recently my sewing machine (Brother CS6000i) has started acting up, such that the lower stitches are pulled through to the top, and the top thread is so taut that the fabric puckers or bunches up. I was able to un-gather the fabric every few inches by pulling more thread through, but that's far from an ideal solution.
It seems like the tension on the upper thread is way too high. If I try to gently pull the thread through the needle, for instance, it takes much more force than usual. However, I hadn't changed my tension dial before this started happening, and cycling through the settings didn't seem to make a difference. This is happening consistently and on all fabric types.
When it first started, I swept out and jiggled various things, which got it working again for a short time, but since then no luck.
Any idea how to fix this issue? Do I need to get it serviced?