Frustratingly unhelpful support resources. For any given issue, the Google team typically offers their canned response, which very rarely addresses the actual issue. Their "solutions" are analogous to the classic "have you tried restarting your computer?" response from PC tech support services. Which is to say, they only ever suggest the most obvious fixes, all of which have already been attempted and subsequently failed prior to reaching out to Support.
Additionally, the lack of basic features that are included in regular Gmail accounts is extremely frustrating. For example, the Google Assistant (their virtual assistant) cannot access your G Suite calendar. The Google Personalized Feed also has numerous problems working with a G Suite account.*
*This is an example of the first problem (the terrible support). The only solution that the Google team can offer is to have the G Suite account admin enable web apps. This is a fairly obvious first step, and one that most admins will have already taken before asking for support.