I did not test with older Unity versions.
Hovering any value when a breakpoint is hit shows the "{} Could not evaluate the value" message (see screenshot below).

Immediately the exceptions in the attached log is thrown.
I tested both with alexzzzz's compiler and with the new Incremental Compiler. I was under the impression that the new incremental compiler could have been the cause, but it was not.
log.txt
I could not reproduce in an empty project.
Any pointers to get better data would be appreciated.
It would help, if you add Rider debugger logs, which can be found via Help->Show log in Explorer. There would be "DebuggerWorker" folder. Zip it and attach, thank you!
Such issue is more Rider one than the resharper-unity plugin one, but I think it is ok, to leave it here.
Ah, now I see we are aware about this problem. No need to attach logs.
The reason is new mono runtime in 2018.2.0b1.
We are working on it.
Fixed this, should be merged in nearest Nighly
Confirmed that this is fixed in the nighly build.
The same thing with rider:
I faced this issue with 2018.1, but after update to 2018.2 everything works fine.
Most helpful comment
Fixed this, should be merged in nearest Nighly