Switch takes 5min to load main menu, crashes when trying to load a game.

Both of my Nintendo switch consoles are taking around 5min to load to the Minecraft main menu, and then either crash instantly or whilst trying to then load a world, giving the "an error occurred" message. Only about 5% of the time will it actually manage to load one of the worlds/savegames. I can be trying for an hour or so to get a game to load on a single console.. 

This is fixed only by deleting ALL save and user data. Once that has been done, the game opens in 20secs, and can createw world as normal. But once I've saved a game or two, the slowdowns reoccur. 

Not using any resource packs or textures. Currently have two completely vanilla save games, one around 80mb, the other 20mb. Some how the save games are slowing the load time of the game down?

I have deleted and reinstalled the game and all save data. Problems reoccur.