Uninstall SNAP 8 and install SNAP 9 that was released yesterday!
That is normal behavior, the plugins have dependencies to newer versions of snap engine utilities than 8.0.0 that you have. Why you are stick with 8.0.0 with no updates?
Plus, as @mengdahl already mentioned, SNAP 9 is released.
Actually, the necessary plugins even of higher version should be downloaded automatically.
Maybe during the download something went wrong.
I have installed the new version and its working now.