I'm on the latest Extended nightly (as of March 28, 2020) with Pak128-Britain-Ex and it seems ships from almost any era (I tried 1920, 1960, 2000) are completely broken?
No matter their power, the max speed is 0km/h. For example, see the modern turbine channel ferry (steam) in the attachment.
What could I do to debug this issue?
I am not able to reproduce this, I am afraid, on my Linux computer. I wonder whether this might be caused by the MacOS change for physics. I have added a preprocessor directive, REVERT_PHYSICS_MACOS_COMPATIBILITY; if you define this, the change to the physics engine for MacOS will be reverted and this may work.