Is it "normal"?

If your husbandry is spot on, no.

If your husbandry is off (fluctuating temps by a few degrees, overhandling, overfeeding, incorrect humidity, too large an enclosure, hides too large, etc), then yes it's normal.

I have 15 ball pythons, not a single one of mine has fasted this winter.

Please provide more details about your set-up (pictures would be best) and perhaps we can help you figure out what's thrown your snake off feed.