Stacking - that is when the thread is wrapping around the needle plate and the fabric is not moving. Yipes. If you notice it right away you can gently tug on the fabric and help it move past the stacking. Or at least avoid the thread knot. But if you have a lump or birds nest - then get the sharp scissors and snip the threads to remove them from the needle plate. If it is a mountain of thread you may have to remove the needle plate and the needles to clear the way. Sometimes this happens because the fabric is not advanced far enough under the foot for the feed dogs to grab it. Of course check the thread path to see that the lower looper thread is not wrapped around something and catching. Another reason is that the presser foot is not down. (been there done that too, so I know.)
Skipped stitches (I may have addressed this before, but it is worth repeating). First check to see that the needle(s) are inserted as high as they will go. Check the thread path to see that you have passed through all the thread guides. Change the needles. Another reason is that the needle thread tensions are too loose or too tight, This you will have to test to determine if this is the culprit. Old thread that has passed it's expiration date. It is dried out and needs to be replaced.
Rolled hem peels off the edge of the fabric - yes it is your fault. :-)
When serging we have a tendency to pull the fabric to the left away from the needles. Try, TRY to push the fabric toward the knife as you pass under the needles. If you are sure you are doing that then move the blade (upper knife) a little to the right to take a bigger bite of fabric. Especially when you are serging a curve it is important to watch the knife and not the needles. Whether it is an inside or outside curve keep your eyes on the curb (knife). The needles know their job but the fabric has a mind of its own and will drift away from the needles and the knife if you are not careful.
Thread keeps breaking and it is the lower looper. Most sergers have an order in which they are threaded. Some upper looper first, some lower looper first, check the manual. If you tie off and pull the thread through sometimes you may miss a thread guide for the lower looper. But let's say that the lower looper thread broke and you just re-thread the lower looper. Ain't gonna work. As you turn the hand wheel the needle threads are wrapping around the lower looper and a knot forms and the thread breaks again. If you want to just re-thread the lower looper then remove the thread from the eyes of the needles and then re-thread the lower looper. Trust me those needle threds love to form knots underneath where you can't see what's happening.
The knife is cutting the fabric but it is catching between the knife and the serged edge forming a sort of ragged knot of fabric. (Not sure how to describe it but hopefully you know what I mean.) Most likely the knife is too far to the right (too much space - a gap) and it may need to be moved further to the left. If that doen't work, then I will grab the tail of the fabric cut and guide it down into the waste receptacle. More often this happens with high loft fabrics like fleece. AND I go slow so I can maintain control of the fabric. Rarely, but sometimes the knife needs to be replaced or sharpened. If you serged over a pin then there may be a nick on the cutting side of the knife. Rub an old pair of pantyhose across the blade and see if it catches - that will be a sure sign of trouble in paradise.
I will give you some more info another time- my brain is tired.