the plasma 5.0 splash theme is inconsistent with the sddm theme. the sddm theme uses regular BreezeBlock Items for its UI however the splash subsequently does an appearance animation with the blocks breaking handover consistency between the login manager and the desktop Reproducible: Always
We still have this animation in 5.5 if I'm not mistaken.
We no longer have it in 5.6 and there's an effort to fix the overall startup experience.