Nintendo Switch players inventory keep disappearing on my realm

I own a realm with my friends. Two of them are Nintendo Switch players. Every once in a while there whole inventory just disappears. They don't die or anything. It's just, gone. When I use a back up to get the items back, the other friends who've made progress in the realm, lose their progress too, causing them to get frustrated. Please fix this bug so I don't have to keep using back ups.