I also get it, and have for several years now. The generic parking page is from my host provider. Usually I notice it happen when I'm actively working on the pages and the site is sluggish to respond. I'll also sometimes get a timeout type error when editing an entry on a page after clicking the update button on one of my forms.
Despite it being annoying, the problem has not been persistent enough for me to reach out to ionos with screen shots of it asking for an explanation. Plus their tech support is lacking options for contacting them these days (opening a chat box is all I've been able to use recently, it works but I would prefer an email option as well). If I'm motivated I'll inquire about it with a screenshot next time it takes place.
