Hi Jeffrey and welcome aboard
I’d start by looking at the controller mappings, as the behaviour you describe might indicate that you have a mapping to one of the elevator commands that you don’t know about. Check that you have the y-axis of your joystick mapped to ELEVATOR AXIS and that none of your other controls are mapped to any of the elevator commands.
Another place to look is in the assistance tab of the settings, to make sure that it isn’t your co-pilot taking control of the aircraft that is causing your problem.
If it isn’t one of the above, then please let me know if there are any messages being displayed on the cockpit display, indicating a rotor overspeed for example, before your helo goes nose-up.