@SM3dLaserInspiration: It is almost impossible to speculate on why a particular listing was deactivated, but Etsy is cracking down on what they feel inappropriate. Reselling and copyright and trademark infringements is a always large factor. Since Etsy is now also factoring descriptions in search, they along with titles, tags, and materials (and possibly even alt tags if you are using them) are all probably being checked. And the bots are also "reading" images. Plus we do not know what combination of possibly multiple factors constitute the trigger that flagged your listing.
As mentioned, you need to include the licensing information (and the usually required attributions and disclaimers) for all of the trademarked and copyrighted names and images in your shop in your listing, otherwise buyers (and Etsy) may conclude they are counterfeits. Including the licensing information will show that you are not selling those items illegally.
Also, the way that you word something makes a difference. "Yubikey BIO / C BIO (FIDO edition) Cover" implies that the cover is made by Yubikey and therefore you are selling a counterfeit or you are reselling. "My Cover for Yubikey" should be okay but obviously the trademark owner can still come after you (if you do not have a license) for using their intellectual property without permission to sell your product, especially if you are not including the appropriate disclaimers and attributions.
