I'm seeing a similar kind of problem where WSJT-X (v2.4.0) will stop decoding if the setup is left untouched for a few hours and is only doing Monitoring. It happens regardless of band. At first I thought it might be something funny coming from JTAlert as I only started using it a few days ago, but with only WSJT-X running, it still stops decoding after sitting untouched for a few hours. Signals are on the waterfall and it's falling normally, the cycle timer is running, the DECODE indicator flashes at the right time but nothing shows in the Band Activity window and nothing shows up on JTAlert. If WSJT-X is decoding, it's not releasing the results.
This does not happen if I'm operating fairly regularly for several hours, e.g. it worked without a hitch over Field Day but now, if I leave the computer and radio alone, WSJT-X will stop releasing decodes after a while. It's lilke some user action on the computer is needed to reset a watchdog timer (I've got the TX watchdog set to Disable).
Now, I know I'm using an older release of WSJT-X, but it works fine for me and I probably won't be upgrading until 2.6.0 is released. Nevertheless, I think there have been other posts here reporting the same problem with 2.5.0 and maybe also RC2.6.
This is NOT a USB/LSB issue. I know what sideband to use for FT4/8. The only way to get things going again is to close WSJT-X and launch it again.
Anyone in the know have any ideas?