1.2.4 patch 1 was at the end of August (the 27th). Similar to 1.2.5 landing on September 30th.You are really not seeing anything to discount September as an outlier?
Its the ONLY month in the last 4 that had no patch, and the drop is caused because of that. Its clearly an outlier and thats why you cant use it as benmchmark, comparing all the other months that share similar variables and context
Of course getting more data in the future will be better to get a pattern, but such pattern will come from comparisons with July and August, not with September
August did have two patches, of course, so the gap throughout September could be significant. But 1.2.5 was also a correspondingly large patch (and included DLC content). Plus the resumption of academic studies across most / all Western countries (if not more). All factors.
So no, I see nothing to discount September. I see factors we can suggest (which may or may not be relevant, I don't know for sure of course), but I see nothing to rule it out.
If "the game needs patches to sustain interest" is the lesson September is telling us, that's not going to be good as the patch cadences settles into a more typical post-release schedule (which typically isn't multiple times per month, for any game excepting live service and / or freemium titles).
The snapshots are monthly, which is why the graph pre-July is so smooth. It's literally one datapoint on the 13th of every month or somethingSteam DB discards data after few months, keeping only peak/average/dunno data per day.

