I think what Tor means is that the Fromeco can get too low in voltage during "heavy" load so that the Weatronic sees this as a low-voltage situation (which is also is...) thereby resetting ?
With the high current draw, it is very important to keep the wires from the battery to the receiver "short and thick" otherwise you will get a high voltage drop, which the receiver will see (correctly) as a "low battery" condition.

I have just (almost) completed a large prop plane with 18 servos in (comp-arf pitts s12), I have two Weatronic receivers already in use in other planes, but for this power-hungry bird I choose to use a PowerBox Royal, as that can supply 40 amps to the servos, the Weatronic is 20 Amps (if I remember correctly..)
The peak current under no load for 2 x 8911 servos for one part of the elevator is up to 13 amps!

One of my Weatronics is in a comp-arf Extra 2.6m, driving 8 x 8711 servos, no problems so far, so I think you will be happy with the 3 and 5 servos