GrapheneOS Yes, I am - and was - aware of that! That's why I emphasized:
harp n RDNS network settings Loopback was activated to log/show RDNS' own traffic, while making sure, participation on "stability program" is off.
I'm using version 0.5.5u from the project's github side. I recognized before that there's a bug in it's settings related to their "stability program" (for which the use Google Crashlytics) - or in the Gui - related to this. If you enable any setting claimed as "experimental" you get a popup informing you this will also enable participation in stability program. After that the stability program setting still appears unset in the Gui. You have to close and reopen the app to see that's suddenly set. In the first time I wasn't aware of that and wondered, why there were appearing exactly these three connections in the RDNS-log: firebaseinstallations.googleapis.com, firebaselogging-pa.googleapis.com, firebase-settings.crashlytics.com. The first one appears usually quickly after the participation is set, the second one quite often from time to time, the third one not that often. But all of these connections are correctly logged as initiated by the Rethink app and appear regardless of charging processes periodically. If the participation setting is set back to "off" manually these connections stop appearing. I was in contact with RDNS devs before on this topic (firebase connections) and they assured the related setting is strictly followed and absolutely no connections to any Google service are initiated by RDNS if it's set to "off". And they also assured that'S what the Loopback-function is for: to log really any connection by the RDNS-app transparent for the user. And these three connections mentioned are clearly logged belonging to/initiated by RDNS and there's no apparent relation to these gstatic-connections.
I see no reason not to trust their statements. Or do you think they don't know or understand how things work they implemented? Or do you have any further explanations, what happens here (if related to RDNS or not)? And why are these connections initiated while charging exclusively (at least in my case)?
So, as described before, these strange gstatic connections (related to this 5-apps-couple) only appear while chargings. In my case it's logged as "MTP Host + other app(s)" but these five apps are the same as here. And again, they only appear while charging/cable-connection.
In addition: In the past I did some large/long file transfers via USB-stick, so a stick was connected to USB-C port and transfering data for sometime even more than 20, 30 minutes. While these procedures these gstatic connections never appeared, only while charging/cable connection. By the way: the original Google charger was always used for charging, a different charger or way to charge wasn't used up to now. But I don't think, a dedicated charger can initiate/trigger this and other models not?