Running the 'Detect' value so low will generally result in random stopping on frequencies that don't appear to have any activity.
For RTL dongles (Blues or RTL-SDR.com), a value of 70+ for 'Detect' I've found the best for these dongles.
The Airspy SDRs seem to work OK at lower values.
A value to low also will result in missing activity as well since it's trying to tune faster than the dongle is capable of.
Not sure if running the scanner with a value to low for extended periods is what is causing the signal to completely drop away though.
I've seen this occurring in Linux where after about 2 days, the RTL dongle (tried a few) goes deaf. I'm yet to determine why as it's using the same librtlsdr driver every other program uses.
Have you tried another RTL dongle to see if same happens?
Have you tried another PC with RTL dongle to see if same happens?
Have you tried a different version of SDR# (say v1716) to see if same happens?
It maybe the dongle playing up, OS, SDR# or plugin. Hard to say.