Cryptomator tries to unlock the vault too soon/before pCloud had the chance to fully syncronize.
Only let pCloud autostart when booting the Computer - then manually start Cryptomator.
→ Auto Unlock works
The permanent solution
Rewrite the code of Cryptomator in a way that it tries several times to unlock the vault on pCloud? That it waits until pCloud is fully syncted?
It would only need to wait a fraction of a second…