This only applies when the console is not connected to the internet.

If I have equipped any (cross-compatible!) skin from any skin pack in a previous session (except Alex/Steve), boot up Minecraft bedrock on my Switch, which is not connected to the internet, and try to load any singleplayer world I get a Platform Restricted Skin error (see image), even though the skins I had equipped are usable cross-platform (e.g. Rancid Anne from Campfire Tales Skin Pack). If I press continue, I can load up the (singleplayer) world normally , but my skin is reset to Steve.

Notable is that the skin preview on the right side of the starting screen is not loaded when I'm not connected to the internet. Only if I connect to the internet, am signed in with a Microsoft account and give it some time to load, the skin preview is visible and I don't get the error anymore when loading a world. If I manually (re)select a skin before loading a world or by pressing the Change Skin button on the error message, I can also load the world and have my skin equipped without errors.

When I have equipped a Limited usage skin like Mario from Mario Mash-Up, I do not get the error when loading a world, and the skin is immediately visible on the right side of the screen when the game has booted up.

I have not bought any skin packs, all skin packs I own were given for free, and some packs were brought over from the legacy Switch edition which I also own.