Variable head speed (external gov)

[cycled]

I have a weird issue on my Protos with YGE 90LV: sometimes on start-up and on switching head speed it gets the wrong speed. Speed is selected via throttle on/off and three flight modes, each with a fixed throttle (something like 60%, 75%, 85%), on the TX, then controlled via a Spirit governor.

In flight the governor holds head-speed reasonably well (not perfectly but reasonably well). On start I use the lowest speed, and sometimes it's higher than it should be, and again sometimes when I switch modes during a flight. But switching between modes can also get it back to the correct speed (in the same flight). Higher head-speed modes may also be wrong but it's harder to tell. It's like the YGE keeps changing its mind about what RPM a throttle value should mean.

I have the same Spirit + TX set-up on two other helis (both HobbyWing ESCs) and previously on another (Align ESC), and none had this issue. I previously had a YGE60 on the Protos and I think it had the same issue. Any ideas?