The newsletter has not been arriving by email (I can still read it on the site).
I went to Substack Support.
After ten minutes of digging and checking things, I ended up with a chatbot.
After ten minutes of chatbot, which told me to do all the things I'd done already, I got this;
"Got it! I've sent this conversation to our team of specialists. If this is about a payment or another urgent issue, you'll hear back from us within a few days. Otherwise please note that due to incoming volume, we aren't able to guarantee a timely response."