There are two common reasons the engine won't hand over control after a start. 1. The engine rpm has not stabilized at idle. The usual reason for this is the pump. Check to see how stable the rpm is after start. 2. The throttle stick is slightly off low. Pull the stick firmly against the stop or reduce the idle trim one click. Unlikely, but I've seen it. If by chance this works, do a Learn RC again.

Less common but I've seen this too. The battery. Put a full charge on it and try again. I have seen starts (but not recently) where there is enough in the battery to start but the end voltage after the start falls into some grey area where the ECU won't respond. When I discussed this with Bob Wilcox, ex JetCat USA owner, he had never heard of it. This was on older engines so I don't know if this applies. I doubt your battery has a problem but worth looking at.

More common: the connection from the engine to the ECU could be a problem. Try a different cable from the other engine. My guess is that this fixes it. Might be why you lost control on landing.