Right, I made a bunch of patterns before and it never really dawned on me to actually download them off of my own Studio when they're used on things like clothes to see if they're working.
For example, I made this cupcake pattern
and used it in this dress
Now, if I download that dress from my Studio this is what I get in CAS:
You can see the pattern is missing in the little style picture, on the dress itself and the pattern also gets replaced by a weird shiny pattern in Edit Pattern. It's categorized correctly though, cupcakes are listed as fabric and so is the shiny pattern.
This is what happened to one of my lots after I downloaded it from Exchange after uploading it:
As you can see in first bit, the patter is gone completely.
In 2nd bit, it randomly changed, most of the stickers are gone or turned white, the frosting went gray and the sprinkles are still in colour, and funny enough in the pattern itself sprinkles and the cherry are the SAME STICKER. So something seriously wrong must have happened for my sticker to be dissected like that.
In bit 3, the pattern is actually still there after, but half the walls received a weird blue-ish mirrored effect.
Also it's worth noting that none of the "borked" wallpapers are actually changeable, I can't even go into Edit Pattern, I simply can't click them...
I have all of my patterns in-game and I am able to manually replace all the borked patterning with the correct patterns but I obviously don't expect everyone who downloads my clothes or lots do the same everytime, that's not how it's supposed to work. The patterns are fine on their own, it's just when they're applied to something and go through the uploading-downloading process that something horrible happens to them.