I agree with you and Peter, it is definitely not RFI.

I lost the output with 1 or 2 watts output from my FT-857 and even lost it while transmitting into a 50-ohm load.  Sometimes I can switch back and forth between tune and transmit and the RF is back.  I also found going to tune then raising the power and the tx snapped in, but these fixes may have been a fluke.  The only real fix was restarting WSJT-X.

The frustrating part is trying to work a new grid, a needed DXCC station on FT8, or an MSK144 Meteor Scatter contact and look up and you're not transmitting for most of the sequence. Starts out transmitting then shows transmitting but nothing out.  I have noticed this issue mainly in RC4 which I just updated to. If it was there earlier I did not notice it.

Microsoft released an update in April 2021 that has just about killed all my computers.  A major MS screwup.  Search for update KB5001330.  It shows many references to Gammers which I am not, but BSOD and slowdowns are a major issue in general.  Now I am not saying that it is this update causing this issue, but it looks mighty suspicious.  I removed that update from my main computer that I do video/audio editing and CAD on it is back to normal speed for rendering.  Again, I am not saying it is that update.  I am running version 20H2 build 19042.948.  I checked that via the Windows key +R  and type winver.  Removing that update can also be a nightmare.  After you remove it Windows wants to reboot after the reboot it reinstalls it as a missing update again.   I can't find that option to hide certain updates.  Apparently, windows removed that option to force updates.  I had to go into Safemode to remove it and then turn off updates completely.

So, is this a bug with RC4 and or a reaction to a Windows update?

Due to the bad Windows updates and the lack of support from Microsoft, Linux may have a future on the computer I use mainly for Amateur Radio.

73's 

Gary N2BRG