We've all noticed on MP the radar warmup is strange now.
Here's how I've always done it:
1. Start engine (battery, fuel pumps, etc).
# go to rearm menu and choose loadout
2. Once engine is running put radar switch on first notch.
3. Switch on the rest of the stuff (HUD, RWR, CMS, NWS, INS etc)
4. Autopilot tests
We used to get the radar available after about 3 minutes I'm guessing, now it seems to start the warmup once in the air or after some other event has fired. I've let my aircraft sit on the ground for many minutes, idling and ready to go, and went to get a drink etc and when I came back it wasn't ready yet. I agree something has changed.