The chained minecarts often run into each other while turning, making them split up and break. Chained minecarts also are very finnicky about the order they were chained in, especially for carts beyond 2.

1.19.2

Unfortunately, 180° turns are problematic because of the way chained minecarts calculate their momentum in relation to the minecart in front of them.
A workaround for now is to make turns 1 rail wider, meaning a 2 block gap between tracks.
I'll look into a permanent fix, but can't promise anything.

That works mostly. The carts will pull themselves off the rail on a turn. The behavior can be noticed if you place another rail next to the track, the minecart will go onto the nearby rail because it is pulled off by the head of the train.