If you sign into kitmaker.aeroscale.net you will be signed into every site on the network. if you sign into aeroscale.com you are signed into aeroscale only. So if someone provides a link starting kitmaker.aeroscale you will not need to sign in, if it is a link starting aeroscale.com you will need to sign in and vice versa.
When I log on to Aeroscale I don't have to log in. When I'm clicking on a link in a notification email and it's for Aeroscale, I have to click the log in every time. But lets say that Torsten posted and he's on NetMaker, I don't have to log in. Next notification is for Aeroscale, and I have to log in again.
I've been here for ages, and never that this problem till recently, and since I haven't changed how I access the site, none of this makes any sense.
Honestly, since others are starting to post that they're having the same issue, the odds are it's something that was changed in the Site's software. If it was just me, then I'd keep on looking at all my settings and cookies.