Jen is used as "Here is" or "Here are" much like voila'/voici in french.

Ĉi tie mi ree estas or Tie ĉi staras mi denove should also be accepted (but without the accusative: being somewhere doesn’t count as moving): they are correct, but the verb can be replaced by jen without trouble :-)

At least, I understand, and I think that most Esperantists also do; so I would totally accept it. Did you report it?

This is accepted now: "Jen mi reestas."