For the last couple of weeks, I've noticed that it's taken me much longer than normal to get automatched. Today, I happened to click on the "familiar cards" listing and noticed that all of the expansions were grayed out. It turns out that my subscription had expired on the first of the month, and since the "wait for expansions" checkbox was checked, I wasn't getting a game until someone who did have expansions came on and looked for an automatch.
It would have been very helpful to get some sort of notification that I needed to renew. I wouldn't have minded getting an email to my personal account; at the very least, how about a message in my game inbox? Something along the lines of, "Hey, we see your subscription has expired. Would you like to renew?" with a link to the renewal page.