I don't usually subscribe to threads but have to one (the USB-C one) just the other day.
My email is on a personal Google Apps account so basically the same as Gmail.
Some (not all) of the subscription thread emails from the one topic are being tagged as spam by Gmail
Why is this message in Spam? It's in violation of Google's recommended email sender guidelines. Learn More
I see the from address is "andy at ...." rather than something like "noreplyatempegbbsdotcom"
I presume an SPF record might fix this but also perhaps better to use the forums domain as the from address too? It's not critical but I thought it would be worth mentioning. I presume private messages would have similar results.