I'm so glad you were able to work out this problem!
I think you should try to stick with the #50 thread, unless you are sewing lightweight fabric. I even will stitch with a #40 thread in the bobbin just because it lasts longer between rewinds.
That may help you get more out of the 50 weight. You should not see any visible difference if your bobbin tension is not too tight.
Last edited by KLKing; 05-02-2019 at 06:13 PM.
Reason: typo