I chatted with Sirius today and they told me that it’s a “convenience” that they offer. If you’re listening to any station that could have adult content it will default to something else (in my case the preview channel) when the car is turned back on. I told him I was on the coffeehouse station when it reset though, so that doesn’t apply. He ignored that and said they do this so that it isn’t playing adult content when the car is started in case someone is in there that wouldn’t want to hear it. I told them I didn’t want this and wanted to change it. He said he had no idea how to turn it off. Chatted with someone else at Sirius who also had no idea how to turn it off. Hopefully someone can figure it out.
This problem is not confined to Nissan vehicles, so it's clearly a SiriusXM problem.
POSSIBLE SOLUTION: Turn your radio off BEFORE turning the vehicle off. Yes it's a PIA, but it's the only workaround that seems to work (sometimes).