I’ve also noticed some weird behaviors with the new GDU370 (“G3X”) and flight planning. The Course indicator will get stuck at 360° N and won’t lock onto GPS track. BUT if you enter flight plan through the GTN530 the CRS arrow will now acquire the gps once you hit the CDI selector on the 530.
The same issue exists in the H125/as350b3. You can enter a flight plan in the GTN650 but it won’t pick up on the CRS indicator. BUT, again, if you make the flight plan in the GTN530 the avionics will connect and you can acquire the course…
Bit of a bummer to enter your flight plan twice so it “looks” right. Because once you enter the plan in the 530, it doesn’t update to the new GDU370. So you have to enter it again just to preview it on the 370, while the 530 controls the CDI.
And the bug still exists, when you start airborne both the GTN530 and GTN430 are black screens.