The 45° FLEXFly doesn't have a diagonal tile at the diagonal end of its CheckTypes, but an ortho stub. This is intentional, and that will most likely prevent the Diagonal-FAMIS curve from being placed right there as a side-effect.
Just curious, does this new version have any of the MHO flex stuff?
Yes. The Draggable Ramp Interfaces for the MHO have been added this release. Just forgot to list them on the features list.
I notice that the RHW-6 exits no longer work as stable as before. With a lot of patience it is possible to click it in the right way. I never see this problems before.
I haven't been able to replicate all parts of your issue (the bit of an inside ramp popping in at the bottom is the one spot I can't recreate--even with running EU textures), but I've fixed some stability with the RHW-6S Type D1, and also with the 90° MIS curves, which seem to have me able to build that setup now without issue.
Is there a way to avoid the new regional transport view colours? I couldn't see anything in the setup (doesn't mean I didn't miss it). I find my streets, roads and highways are all essentially black (whereas the legend indicates roads should be grey...?), and it makes it hard to glean much information from it. Thanks again. 
The RHW-compatible Regional Transport View Plugin requires that the user open up a DataView at some point before saving the city tile. Doing so will actually change the colors to something more fitting, rather than all black (and unfortunately, changing those more fitting colors is not in the cards--
jondor chose those very specifically to cover up what you encountered.
More details on it can be found in
this section of the documentation. It is possible to select to not install it, but doing so will mean you won't see RHWs on the Regional Transport View.
-Alex