Upgrading Project to Higher Unity Version Break downs animator transition links

Hi guys,

I am having a weird problem with animator.
I recently upgraded my project to a higher unity version, however for some reason the transition links between some stats disappeared and i can't add them either. Unity wouldn't allow me to add them.


I did step by step upgrade, from Unity 5.4 to Unity 5.6 and it worked, from Unity 5.6 to Unity 2017.1 and it worked, from Unity 2017.1 to Unity 2017.4 or Unity 2018, it breaks down. It works right up to unity 2017.1.0, but any upgrade after that breaks down the transition links between stat machines.

Has anyone come across this problem before?

Any help would be appreciated.

Regards