Can confirm in release 1.15.1 (the seed above doesn't work anymore but the same outcome still occurs with any seed).
Yes, I just checked and this is still an issue in the latest versions.
It looks like summoning any entity will crash your world.
Okay so this is not actually a bug. Just a mistake on my part. In the entitydata command, I had the Count set to 1. I guess this was causing the stack to change into only one item. So by removing the Count tag, the amount of items is not effected. Sorry about that!
It will show two items on the ground, but I only count two when the items are picked up, even if I summon more than that. After I summon more than two, it will still only show two items on the ground and I'll only be given two in my inventory.
I think this may finally be fixed in 1.16.4! I updated the provided seed and coordinates. Generating the world with Generate Structures set to off did not generate the dungeon at the provided location, as (finally) expected.