However this is not a single word, but would be split as "allzu regelmäßig" cf. https://www.korrekturen.de/wortliste/allzuoft.shtml
Well, then it seems we don’t have any single German word for all too regular anymore :(
My new proposal would be überregelmäßig. Über+adjective is still one word only, post-reform. Sounds strange, but grammatically correct, and still conveys the “unusual” part.