“From the limited information The Tor Project has, we believe that one user of the long-retired application Ricochet was fully de-anonymized through a guard discovery attack.”
The user ran an old Ricochet build without Vanguards-lite or the vanguards addon. The maintained fork has had the protection since June 2022. The Chaos Computer Club got the case documents. The Tor Project got a vague outline and had to go public to ask for the rest.