And it has it been a rather stable load since then? Or is it still growing?
(the public history only shows the current year 2019, so it is hard to see if there has been growth in Sep/Oct/Nov/Dec/Jan.
If it is rather stable, it reduces the probability of gradual firmware updates by individual customers, or something like that, (causing a growing load along the growth the installed base of the new fiirmware with this test download site).
That being the last day of a quarter (or one day before the first of a new quarter), I have a guess:
some kind of SLA that has been automatically tested since 1.10.2018. E.g. automatic connection speed testing every few hours, run from customer data centers (or modems).
(or the remotely controlled test URL has been changed on 30.9.2018 to point to our site)