UPDATE to preface: It actually looks like this is a duplicate of REALMS-2195 – the difference being it works fine for me on the Realm, regardless of whether I access the Realm from the Switch or Win10. It doesn't work for anyone else using Switch or Android. I also just tried with my account on an Android phone. It prompted to download the pack when I joined the realm, which I did, but then it didn't apply it; it was still the default. So exiting the Realm and enabling the pack from the Global Resources menu caused me to download it again, and now Minecraft crashes every time it tries to load the menu.

Preface: While some existing tickets were sort of relevant, none seemed to match my exact issue

I purchased a texture pack called ChromaHills HD. I uploaded that texture pack to my realm server and it works great on my PC. I then logged in on my switch, downloaded the texture pack, and it works great on the switch.

If my family members try to join the realm, using the same physical Switch, the texture pack will not load for them. It loads the default texture pack with a lot of purple/black square texture (I assume that denotes the texture is completely missing?). I can then log out from there account and into mine on the Switch and the texture pack loads OK.