Update: Turns out this probably has to do with the new onboarding process for the Reddit app. You can see similar increase in subscriber counts for formerly stagnated subreddits like /r/atheism as well. Thanks to /u/jippiejee for the info.

I noticed that /r/fffffffuuuuuuuuuuuu recently started gaining subscribers at a rapid pace despite four whole years of losing subscribers slowly as seen here. At first I thought maybe this could be explained by students being off school for the past two months, but I doubt that's the case because summer didn't affect the subscriber counts in any past years. I'm not aware of any algorithm change in the past few months that could cause this, but please correct me if there were.

However, even if that were the case, I feel the increase of about 100,000 subscribers in two months would be reflected by an increase in activity, but it's not. The front page still has a post, not even a particularly popular one, from 27 days ago. If you check back to when the growth started two months ago, you'll find only 39 posts have been made in that time, meaning less than one per day. The craziest thing is that total number of upvotes on those posts is less than one third of the subscribers gained in that time (I'm not actually sure if this is normal but I don't think it is since Reddit stopped vote shaving as much). Because of this I think the growth in subscribers is possibly artificial.

I find it especially suspect because there is a period of from the 21st to the 24th where no posts were made, yet in that time the subreddit gained at least 5,000 subscribers. The only thing I can see causing this is popular thread linking to the subreddit, but the growth is in line with what it has been for two months so I doubt it.

Anyway this is just something I noticed which seemed weird and wanted to see what someone else thought about it.