Student or Learner
I'd like to know if the sentences "I can't keep up with what you are saying" and " I'm not following what you are saying" have the same meaning, and if they can be interpreted as the speaker is not being understood or he is speaking too fast.
"Can't keep up" implies an ability to understand, but a problem with the speed.
"Not following you" does not say anything about speed, but about comprehension. If you say you're "not following me," I would try to re-phrase not slow down.