I use Universal GCode Sender. and I had the exact same thing start happening yesterday. I probed several times using my macro in UGS using this command - G38.2 Z- .5 F1 and it worked fine. Then all the sudden I started getting a GRBL Probe alarm when trying to probe… And I noticed it was probing up instead of down. I tried power cycling the controller, restarting UGS, etc. But what fixed it for me was to add a G20 G90 in front so my probe command is now G20 G90 G38.2 Z- .5 F1. Now I am probing in the correct downward direction again. I am using the UGS 2.0 Stable build. So you might try adding a G90 in front, which sets it to absolute position mode.