If it's the package of needles you should be able to find something when comparing to a good one; needle hole slighly off it's spot, maybe a burr some where or not as polished as usual, the grooves and shape of a needle need to be made to a high standard. A worn neede is something you can check for; run the tip over your finger nail or nylong stocking at it will catch, a new one will feel smooth from all angles. No need to bin a package of perfectly good needles.
Dust, lint, bit of thread, etc. caught in the bobbin-hook-feed dog area can disturb the interlocking of the two threads, very basic but it can happen on any machine.