Your sewing machine is eating the end of the seam. The problem maybe that the needle or the opening in the throat plate is too large. The problem is very common if you are sewing very small pieces of fabric.
A very simple solution when youve already tried a smaller sewing machine needle is to abut a scrap of fabric to the beginning and end of your seams.
The scrap will fill the void left at the end of the seam and should avoid the machine eating the end of the seam.
Another solution is to use a vanishing stabilizer under the fabric you are sewing. Heat away stabilizer, which turns into dust when heated, is especially good because it is relatively firm and less likely than other stabilizers to be pulled through the throat plate of the sewing machine.