Timeline Assetbundles Unity 2019

Hello,

We are trying to switch from 2018 to 2019 and are experiencing a problem with assetbundles.
Our assets bundle are built on 2018.
In our assetbundles, we use timeline to run animations.
When running the project in 2019, we see warnings of `missing script reference` and non of the animations are working.
I'm assuming its because of the change to where timelines resides (in a package vs part of editor)
Any ideas how we can fix this? we really want to move to 2019.
rebuilding all our assetbundles with 2019 is currently not an option.

EDIT:
just found this post:
https://forum.unity.com/threads/needs-update-assetbundle-with-unity-2019-1.681946/
is there really no solution for this other then rebuilding?

EDIT 2:
I tried looking at the YAMAL files of a .playable and also a director component on both 2018 and 2019.
I could not see any difference in the files.... so how is this not working?