Bingo! - as
@oaken1 said.
It means that Simmons most likely are showing more that your average UDFA/camp body and they want to test it out. Doesn't mean that he makes the team or is on trajectory to start.
Means that the coaching staff likes the development prospect of him and testing if he is so good that they need to statch him away.
He is so good that they need put him on the active roster, so no other teams steals him like they did with Weaver or Gaines?
Does he get injured that for some reason never heals and he ends up in IR for the entire season like Elijah Jones.
Or can they convince Simmons of the developmental timeline and put him on the Practice Squad where he would want to stay and not sign with other teams?