If you have updated recently both plugins, it may be difficult to identify what is causing the problems.
I must say that Corona 5 is very recent, and we have not tested it yet.
Regarding RailClone 4, we implemented many changes, but it has been tested extensively while the beta, and actually we have not known issues regarding stability.
I would suggest you try temporary RC 4 with Corona 4, to see if there is some difference. In the next days, we'll make our tests with Corona 5.
Regarding the Interactive Rendering issues, unfortunately 3DS Max plugins were not designed to support IR, and some problems may occur.
For example, RC objects dissapear from viewport (this is a known issue). When possible we try to implement workarounds, but there are limitations.
According to the Corona team, one option that may help for stability is to enable "Lock 3ds Max during render" (at Render Setup->System->System Settings).
Do you test your plugins with latest Autodesk stuff or it is written to be compatible with versions older than latest one.
Normally we test our plugins with the latest Max versions (actually 2019/2020), but previous versions should work fine too.
What would your advice be regarding the version of Autodesk?
A good recommendation is to wait some time when a new 3DS Max is released. For example, until the first Service Pack is available.
Are you working on update for Raiclone fixing the problems with Corona ?
As said above, actually there are not know issues with Corona 4 (expect the the peculiarities of Interactive Rendering). Corona 5 is very recent yet.
What is the best way to share a scene with You so that You can investigate?
You can find here
instructions to send us your scene and minidumps
But please note we only can investigate problems which are reproducible.