Knit beanies when embroidered either need to be used with a topping (such as water soluble topping) or use a lattice motif underneath (in the color of the substrate to help "hide" the motif) to help stabilizing the hat.
Applique twill could also be used (but more expensive as the process is more involved, but an option none the less).
Now, you could over compensate with really overdoing the fill density, but that can be no bueno in it's own regard.
Dealing with knits is not the same as dealing with other types of substrates.
Without actually seeing the file itself, it's hard to say if it's digitizing, embroidery or a combination of both.
In most instances (unless talking about puff or other specialty applications) digitizing is a good place to start, but that only goes so far. Sometimes people need to use specialty stabilizer (or adjust regular stabilizer use accordingly), use certain needle for the job at a hand, slow the machine down etc.
Did they try to use one file for a multitude of substrates? While in some instances, that does work, if the substrates are opposites (say twill for one item and silk for another, rarely that extreme, just to illustrate in this case), one file isn't going to work. Not unless a lot, and I mean
a lot of work is done at the machine to make it work. Even still, it probably won't work. Silk isn't fun to deal with on it's own.
We don't embroider here, but that looks like a pretty detailed image to embroider on a hat. Unless it's a really big hat.
Beanies you can actually get away with more size (in most instances) then with say a ball cap. I typically don't go over 2.5" in height for a ball cap (low to mid profile, rarely get trucker style hats), but you can almost get an LC size with beanies. Some styles you can't, but on some you can.
