I configured both to be 30104 and they worked for about 4 hours then the next day stopped working. I them re-configured them both to 30004 and it hasn’t thrown any more errors as of yet. Not sure if why 30104 stopped working or why it wont work now.
I would guess that you have another dump1090 version running (with a different configuration) that’s competing for the dongle. This will be obvious if you look at the logs as I suggested.
If it is happening, it will be obvious from the logs. What do the logs say at the time when you saw problems? I mean, dump1090 doesn’t randomly change its port configuration for no reason so obviously something is going on there.