Minecraft nintendo switch: why can't I join some friends' worlds?

I sink minecraft on the nintendo switch and only have the problem that I can't join some friends (not all)! It loads for ages and then there's something like "no connection to the world" please urgently for help as I can't find any information about it anywhere

It is quite possible that your friend does not have a stable internet connection or one that breaks down often. Otherwise you have to consider that you can only play on the same platform or via cross play from Switch to Xbox

Thanks but the internet connection is stable and we both play on the switch

Does your friend live nearby?