Why did Unity break Rigidbody Interpolation on 5.6 - it worked so perfectly up until then?

I am stuck on version 5.5 because 5.6 breaks rigid body interpolation - so weird to break something so fundamental to 3D games programming. The fix is apparently 2017.1 but I have tried beta and it distorts and twists some of my animated models so looks like 5.5.3p3 is the last good build. This unfortunately means that I can not build Android as Vulkan and also that the new IAP won't work because they require API24 for targetSDK and 5.5.3p3 does not support API 24 - wow after 3 years of work I am so frustrated by this! Does anybody at Unity know when this will be regressed and why it was done in the first place.

"In order to call GetTransformInfoExpectUpToDate, RendererUpdateManager.UpdateAll must be called first."