PotionEffectType#getName(), which has been deprecated since the move to registries returns the old API name of the effect type for potion effects with IDs 1-33. However, the counterpart static method PotionEffectType.getByName() - also deprecated - performs lookup against the EFFECT Registry and will return null for PotionEffectType#getName() values where the old API name differs from the registry key value. This breaks backwards compatibility with plugins saving potion effect types by name.

For example, PotionEffectType.HASTE#getName() returns "FAST_DIGGING" (as per impl) - but PotionEffectType.getByName("FAST_DIGGING") returns null, because "haste" is the expected registry name.

Suggested solution would either be to have getName() return the key value name for IDs 1-33 (may introduce breakages) or have getByName() support legacy lookup (it's deprecated anyway, so may be better for back-compat)