Hi Novato,
I have no idea what is going on with IVAO - we made the TCAS to show the targets as available in X-Plane (AI aircraft) with those datarefs. I thought it was working with VATSIM and IVAO as well, if it isn´t then that would be up to the IVAO client to emulate correctly, I think.
VNAV descents can be quirky, that is a known issue. Pretty much the only descent profile that works well is a normal descent from cruising altitude without altitude or speed restrictions. Entering restrictions is possible, but VNAV will likely not follow them. If you encounter problems with the VNAV calculations, revert to a V/S or FL CHG descent to meet the mandatory restrictions. We are looking to improve this in the future!
Look here, the last point in the "FMS" section: https://forums.x-pilot.com/forums/topic/8526-things-that-are-not-going-to-be-in-v133/
Cheers, Jan