I must be odd that I insist all my lens or body self timers work. From Rolleiflex, to Hasselblad, to Exakta, Leica, Nikon, Canon, Minolta, even Voigtländer Bessamatic. Everything.
Once the self timer fails, the next are the slow speeds. It's an indication the lens or body needs a CLA.
(*) I apologize for the butchered use of Greek. However, I just now learned the difference between Kairos and Chronos.