LTS has had major breaking changes in various areas in recent times too, virtio was badly broken at one point this year, as was a commonly used netlink interface. Hat tip to the Arch kernel contributors who helped track this down and chase upstream, as we had mutually affected users. The debian and ubuntu bug trackers were a wasteland of silence and user contributions throughout the situation, and frustratingly continued to be so as AWS, GCP and others copied their kernel patch trees and blindly shipped the same problems to users and refused to respond to bugs and emails.

You're right stability comes from testing, not enough testing happens around Linux period, regardless of which branch is being discussed.

It's not easy testing kernels, but the bar is pretty low.