I have that problem also but only when I want to join another Switch Multiplayer game. (Reported it here: https://bugs.mojang.com/browse/MCPE-34633)
Loading a world or creating a new one works just fine.
I tried to play around with the graphics settings, used the regulare ressourcepack and the Nature ressourcepack. Nothing helped. And when I want to go into the settings menu the game crashes completely.
Too bad. We heave to Switches and want to play together but it's just not possible.
Submitted two more screenshots via Twitter:
https://t.co/6D5odVOhRN
When using the same graphic settings as the host and shutting of the Texel-Antialiasing sometimes I can play and it runs. But still the game crashes when I want to open the settings menu. And the loading screen looks weird again. Please a look at the screenshots on Twitter.
I have a bad feeling when playing like it all can crash every moment.
It's different on our two Switches since 1.5.1.
1. I open a game on my Switch. My wife joins. Both have the regular and the Nature ressourepack in the global ressources. That way it works pretty good with 1.5.1. The pink/black textures are gone. But still the screen is not displayed correctly. The black background is too narrow, the items in the Crafting menu and inventory have a brighter background and so on.
2. I tried this: Both use only the regular ressourepack in the global ressources. But my Switch loads the world with Nature textures nonetheless. When my wife then joins my game the pink and black attack is back on her Switch... Which is weird. One should think that the regular textures work fine.
But we will try more tomorrow. If Case 1 works fine for us we will go that way. It's playable at least. But I hope another patch is in its way.