Hmm.. I haven't heard of anything like that happening to a Tamagotchi Angel. It could be a glitch, but other than that I'm not really sure Have you tried researching it?
There are rarely any glitches, if any at all, in any of the ancestor Tamagotchis. This is just the way they evolve, not like the connections, which go through a first evolution after 2 years. I have an Angelgotchi and evolving into the stage in question at 4 is pretty normal. Have fun!