I*ve had a 2019 Sig for 9 months and my experience pretty much mirrors everyone else. I*ve worked with Sirius, been to the dealer 4 times and contacted Mazda customer service. The software was updated to version 335 which seemed to have no effect on the problem. I can*t see a pattern to the inability to connect with Sirius (other than the free channels), and it always requires a vehicle shutdown of some unknown, but lengthy period to re-establish communication with all the Sirius channels.
The failure mode was slightly different earlier this month: Instead of just displaying the Sirius channels on my Favorites screen with me unable to select them, it gave me a series of screens: *Connecting to Sirius radio* , *Unable to connect to Sirius radio*, *Check Sirius Tuner*.
As others have mentioned, I*ve learned not to give it any commands until it finishes booting up which takes just over a minute from a cold start and about half that if I have just stopped the car for a short time. I don*t have it load my iPhone contacts as I have been told that doing so will only slow it further. It does, however, seem to boot up faster if I turn the Bluetooth off on my phone.
The 10 year old car that this Mazda replaced had none of these problems * it*s really inexcusable for a new car.