I haven't heard about such issues from the French community and here in Spain I haven't had any input lag for months. So yes, without much investigation its look like an issue from a connector in Germany. And a part of internet infrastructure isn't managed by local ISP, failure could come from so many places...
Dunno if possible but if all impacted users could share their location on a map we could maybe see a pattern.
We are spread all over germany, it's different ISPS who have that issue. In my Opinion it must be the netcode.
There is only one ISP, which doesn't have that issue at all.
And even some germans didn't have it, but it spreads. Sturmpanther didn't have it, now he has. Polish People and Czech People..even some dutch players.