With SKS fenders, the chainstay bridge clip was a POS. I drilled a small hole through the fender, 1cm from the end and zip tied around the bridge. The mount has remained solid for several years daily use.
What is the deal with a vertical hole through the seatstay bridge of the Sirrus. Is it simply a mistake or are you meant to bolt the fender to the frame. My steel forks have a special threaded tab at the base of the steerer to bolt the fender directly to the fork without any mounting metalwork.