What are the subtle semantic differences in the following three tri-part phrasal verbs:
(1) be up against (2) come up against (3) run up against
The differences, I think, are mostly aspectual rather than semantic. That is,
None of these is written in stone; they are tendencies only, and I think you may safely use any of them in any context and they will be perceived to mean exactly the same thing: you’ve got a problem.