Can't remember the exact PAW limits I've set but they have been unchanged for the last 2 years at least, ditto the tablet. Evening before last I had several contacts visible on tablet and phone screen including two in the red, one 300 below and one same level but somehow the tablet is not generating the audio alerts for traffic despite being set to while producing audio for everything else.
I have known settings change or for the settings to be lost.
If you are getting traffic alerts via Skydemon then there should be no limits set in the PAW, AIUI. The PAW sends everything and the limits are set in Skydemon?
Sometimes software updates change things or reset values, but this does not explain why it might happen that you lose traffic mid flight.
A lot of fault finding involves elimination, and the first thing I would eliminate is the software settings in the PAW and SD.
I'm looking at SD now and the audio alerts for trafifc are set separately from airspace, obstacle and terrain. So it is possible to have traffic verbal information unticked, hence no traffic info, and yet all the other warnings working.
YMMV