In other articles about that I read that this is related to a software component called "System T7". There was a very similar incident in April related to that component.
Xetra, Eurex and their T7 users Wiener Borse, Budapest Stock Exchange, and some others were halted most of the morning - luckily the stocks can be traded elsewhere, but the derivatives not so much.
I'm not sure about the particular component but Xetra/Eurex indeed went down in April. Same pattern as today: it went down around the opening hours and got fixed around lunch time. They have some structural problems that have likely been left unsolved.