I was using a relatively unused Singer that had been in storage for a number of years. I was attempting to sew across a double layer of webbing when I hit a D-Ring which caused the forward progress to cease. The machine would not pick up the bobbin thread after that. The man at the Singer shop said that during the long storage period the timing belts had loosened and when I hit the D-ring the machine "skipped time". He fixed it. All's well that ends well.
Sometimes even a Blind Hog finds an Acorn