It is an issue with the earlier units of the F8 indeed; as acknowledged by Zoom, they changed some RF shielding design in the later production runs, as well as with the F8n. I can say from my (still limited, not tested throughout due of lack of time..) experience that the later Zoom 8s don't have this issue. Other recorders I or others tested/are using with success; Mixpre 10T, SD 633, Sonosax SX R4+, lower cost Zoom devices, Zaxcom Nomad. Like I mentioned before, we had interference on the Lectrosonics SRc receiver when in close proximity, but in the same bag there was a Sennheiser G3 RX and that one didn't had any problems.
Extra note; the fact there is "RF spill" or how you wanna call it, is the fact there are 2 transmitters in the receiver as well, for the bi-directional functionality. As with all systems, that might explain the problem with the Lectro unit, since it is a known fact that TX and RX close to each other is not a wise idea.