@Joseph M. H. Hmmm, no service flow diagram on this (type of?) problem? Problems > Problem X > Impacted Service > gets me to a page with Understanding Dependencies and an Analyze Backtrace option but no View Service Flow option.
Go to Transactions & Services (left Menu) -> Unmonitored Hosts -> Response Time
Then scroll down and a list of these hosts will be displayed.
Is it possible that there are calls from hosts in one Env to hosts in another Env? Environments separate completely. Another option if there really are calls across Environments to instead use Management Zones, which if you have access to both zones you'll be able to see data across Zones. I'm just not sure this is really what you want however.
Let me know if you find the list of 'unmonitored hosts'.
Feeling intensely stupid. Left-menu > Transactions & Services. Column 2 shows next-level options grouped under headings: State, Scope and Usage, Service Type, Service Technology, Request Attribute and Tags. None of these groups have an "Unmonitored Hosts" option. Nor can I find the version of DynaTrace we're running internally, in case I'm having an "old UI" problem.