I have a Juki 98TLQ and it's a workhorse. It's very strong so the thread has to be strong. I can not sew with any of the invisible threads - snaps the thread every time. Coats and Clarks works just fine in it as does the cone thread.
My Babylock Espire sews with all the thread I have and I have quite a collection.
Sometimes it's not the machine - it's the fabric you are trying to sew. I found out that when making my husbands t-shirt quilt that the only invisible thread that did not break was the Sulky brand. Trying to sew through t-shirt material with the pellon fusible was difficult.
And then sometimes sewing with the wrong size needle for the fabric you are sewing. I always keep my manual handy and if I have a problem with sewing start checking for the problem.