It's the 5.8Ghz antenna (used by the analog receiver and also used by ocusync 2). If your Mavic 2 or P4Pv2 is set to 5.8 exclusive, or it's set on auto (default) and flips to 5.8, you're very likely to loose the video stream. The 5.8 ocusync range without the antenna installed is about 300m.
Having antenna uninstalled in any RF transceiver does cause reflection of the output signal back to high frequency amp.
But the power used in CE or FCC certified consumer devices is not enough to fry the amp. It will disperse a bit more power, so will get a little hotter, and that's it.
(that's an old post; but it seem to be resurrected every april/may)