You are backwards with your expectations for new software as it pertains to the majority of open source projects, including Ubuntu. You expect new software to have more stability, but generally the opposite is true. Older software (that is still maintained) is generally a lot more stable.
The newer the software, the less testing it has undergone. Typically, the newest versions of software are still in development, beta, or pre-release. Even when new versions of software are fully released, in many cases they are still called "bleeding edge", called such because you might get cut.
In terms of the Linux kernel, Ubuntu publishes its own version of the Linux kernel that is tested to work with Ubuntu. For LTS releases, there are two choices for kernels: the GA kernel which is an older kernel version with more testing and stability and a HWE kernel, which is a newer kernel, aimed at supporting newer hardware and features, at the risk of slightly less stability.
But when you decide to go away from the Ubuntu kernel completely, you are adding even more risk of instability, because these kernels are not tested to work with Ubuntu, nor does the Ubuntu development team have any ability to solve issues that might be specific to Ubuntu.
In short, the latest is not the greatest in terms of stability.
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