@splitice Thanks for the replays,
Re the second replay, the issue is compatibility with one of your mods. M27 will currently only apply engineer logic to land engineers, but after doing some debugging it looks like the mod combination you're using results in the normal engineer blueprint (e.g. uel0105 for UEF T1 engineer) being modified to contain the air category instead, which I'm presuming is the Flying Engineers mod. I'll add in a fix in the next version so M27 will try and build stuff/use the engineers where it detects this mod or can't identify any T1 land engineers that are buildable, but it's likely there will still be some unintended sideeffects/interactions.
Edit: Checking the first replay it's the same issue as the second (with the flying engineer mod causing issues) - this will be fixed when v40 releases