I think I figured out at least part of my problems with the RT610 yesterday. The communication problems always begin last in a session, when the battery is at half power or less. I don't know why I never noticed that before, but that's when it started yesterday, and all of a sudden I rememered that is when it has always happened in the past.
It still operates with the lower battery level, but it loses communication frequently. More and more as the batter gets even lower.
Since I am happy with the system otherwise, for the most part, I guess I will get another battery.
Looking thru photos from yesterday, and the more I think back about previous experiences with the RT610, TTL also becomes less reliable when the battery begins to become depleted.