I'm NOT trying to scare you by saying this ... ok?!
I could be totally wrong & it could be something totally different causing it ...
but when my machine started doing this very same thing = not filling in where it should have been = the embroidery arm was "OFF" and basically had to be replaced. ("arm" = the part that grabs onto the embroider hoops & helps move it around under the needle, if it's not moving in time/right = the stitches don't fall where thy should have.)
In my case (singer XL-6000), I could just get a new embroidery unit & it clicks back into place, on the machine's base unit, like the old one did
And thank goodness it was still covered by the warranty ... IF it had happened about 1 month later = I would have been looking for "miracle money" to get it running again ...
The ONLY time we think MIGHT have gotten goofed up / caused it to do this = was one day it was running on its own & my 3 yr old walked by, looked at it weird for awhile, then reached out & stopped the arm from moving for almost 30 seconds ...
The machine reeeally didn't like that = flashed some weird error on the screen, rebooted and SEEMED FINE = but about 3 days later, it slowly started "going off track" like the example you showed.
But it was weird! It would act fine on simple lettering and flowers, etc. (mostly pre-programmed stuff was fine & some custom designs, but not all) = but anything that reeeally had to be lined up over & over like lines around a color or whatever = it would freak out again ... I had to go to TWO warranty centers before I found someone that had seen a machine do this before & knew why.
Just thought I'd share ...
IF it's not the artwork/embroidery file itself = I would almost bet money that it's probably the embroidery arm ...
PERHAPS CONSIDER : check your warranty ... &/or check to see if you can return or exchange it for a new one right away.
Sometimes, the big repairs like that, are simply not worth it, since a new machine is cheaper than the repair bill ...
good luck ...