Could you attach logs from device?
To my knowledge RhoMobile supports ios 7.x and Android 4.1-4.3 (JellyBean). Please see the release notes http://rhomobile-suite.s3.amazonaws.com/4.1/4.1.1/RMS_0401xx_ReleaseNotes.html https://s3.amazonaws.com/rhomobile-suite/5.0/5.0.2/RMS_0500xx_ReleaseNotes.html In future version, they will support ios 8.x and Android 5.x
Rhodes 4.0 was written well before iOS8 and Android 5 were released. It's awfully hard to impossible to write software that will work with some other software that does not yet exist!
It is not difficult to update from Rhodes 4.0 to Rhodes 5.0, so I would try that first. It is nothing like the difference between Rhodes 2.2 and Rhodes 4.0.