I did smoke-test of 3.5.5 and 3.6.5 for Hexacopter in simulator, GUIDED mode mainly.
Its EKF signals failures either before takeoff or during the flight.
No matter how HEXA frame is modified, all the other parameters are default (taken from quad defaults).
Same test with quadcopter frame produces no issues, EKF without warnings or malfunction.
Only hexactoper fails during the takeoff or its flight is way off the track.
Q: Does anybody experience the same problem using HEXA and SITL?