I spent some time trying to trouble shoot a simple sketch with one MEGA talking with another MEGA which was producing occasional "nothing..." errors. I recalled that I have ordered some RFM69HW_HCWs and some RFM69W/CWs. On one of the units I uncommented for RFM69HW/HCW and that appears to have cleared up my errors.
I imagine if I inspect the RF chip it's indicated there somewhere, but my MEGAs are installed in projects and the RF chip is not visible. Is there some other why to tell which transceiver is attached? In future, of course, I'll pay more attention to what I'm installing.