I've got 2017 installed on my machine and installed 2019 as of yesterday.
I've had the live version of FP and RC on my machine to begin with but then went and installed the Beta versions *just* for the 2019 version of Max......
That caused my 2017 to have all sorts of issues, script errors all pointing to RC and FP, even though I wasn't even using either of those plugins in 2017, just trying to move a spline (in fact a single spline was all there was in my scene).
I could only see one solution to try and that was to re-install the previous Live versions of FP and RC back into 2017 - that fixed things.
(I haven't gone back into 2019 to see if FP and RC still work in there as too much is still not working in 2019 to be of any great benefit at this early stage).
So, I'm just saying, that you might need to do something similar if you have previous versions of Max and FP and RC installed and you try installing those Betas for 2019.