It appears that the (help) procedure (from `ice-9 session` can't provide help information for modules that are imported with a prefix.
Normal module import:
scheme@(guile-user)> (use-modules (system vm trap-state))
scheme@(guile-user)> (help add-trap-at-procedure-call! )
No documentation found for:
(system vm trap-state): add-trap-at-procedure-call!
scheme@(guile-user)>
Prefixed module import:
scheme@(guile-user)> (use-modules ((system vm trap-state) #:prefix ts:))
scheme@(guile-user)> (help ts:add-trap-at-procedure-call! )
Did not find any object named `ts:add-trap-at-procedure-call!'
scheme@(guile-user)>