OH4 migration rules fail but work if type: application/javascript;version=ECMAScript-5.1 added

I used the mainui to install Nashorn addon.
The javascript remove was because it was getting warning saying it was being ignored. found it here: OH4 install issues

Am I seeing all of these problems because I am upgrading from 3.4.4 to 4.0.0.M4 and other people are gradually upgrading via milestones? EG going from M1-M2-M3-M4?

I am using a VM and have snapshot so I can go back to 3.4 and try different ways to install.
I will persist and see how I go.