I have a similar problem. I haven't completely solved it yet, but I have discovered some interesting findings. Maybe this will help someone. I'm glad you found the cause in editor.autoIndent. But it still doesn't solve the problem for me. So, I'll leave the information here. In my case, the “indentNextLinePattern” is not working.

1 - It is strange that you expect a single “increaseIndentPattern” to work. My experiments and reading the information showed that it doesn't work alone. It needs a pair of “decreaseIndentPattern” to work. Even stranger is that you wrote “Then I discovered that I had ‘editor.autoIndent’ in the settings.json file: “none”, which was the problem.” - So just by enabling “editor.autoIndent”, you got the single “increaseIndentPattern” rule working? Without its “decreaseIndentPattern” pair? That's very strange.

2 - Expressions like “if (3 > 2) {” have no meaning here. The thing is that VS Code automatically adds indents if you press “enter” after an opening bracket. This works even if no separate automatic indentation rule is defined for the language. It works for brackets (, [, {.

3 - That said, in my case, the “increaseIndentPattern+decreaseIndentPattern” and “onEnterRules” options work. But “indentNextLinePattern” does not work. That's the weirdness.

4 - Neural networks help well with regex. The same Chat-GPT, Git-Hub Copilot, Perplexity, Claude. They are also good at explaining the principles and design standards of language packs. With neural nets, I was making fast progress in creating custom language highlighting. Until I got stuck with this weird problem with “indentNextLinePattern”. All in all, I created the bulk of the highlighting in about 3 days. Polishing and working out the details took me another week or so. Without neural networks, I would have been sorting it out for at least a month. And most likely, I would have quickly abandoned it because of the complexity and intricacy of the topic. Many thanks to neural networks. I love them very much.