Removing from set doesn't remove from other devices, causes re-add

[joshbirnholz]

I have a countdown app that allows you to put countdowns into different categories. The Category class has a to-many relationship with a Countdown, so a countdown can be in more than one category, or none.

When I add a countdown to a category, it gets added to the category on other devices as well, just as I'd expect.

However removing a countdown from a category doesn't work correctly. Removing a countdown from a category triggers a sync. On the other device, a sync is triggered, but the countdown is not removed from the category on the other device. Another sync then occurs on the other device, which then triggers a sync on the first device. The countdown gets re-added to the category on the first device.

I'm not sure what I'm doing wrong or what's causing this.

Videos of this happening: https://imgur.com/a/5759Ae6