Ah, so your webadmin … Well I saw your post on the chat or something earlier yesterday I think, you may want to look at Google flags my sites as dangerous (Deceptive site ahead)
TL;DR : google has some tools (also included in Firefox) which flags website according to a bunch of criteria, and there’s actually no simple way to know why / what exactly makes it so that yours get flagged … Naively I would think maybe .dev is an uncommon TLD but that’s a rough guess