NF DP/Flex ruling

[slapperdad]

NF rules:
F1 is the DP
F9 is the Flex

F1 gets a base hit in the top of the fourth. Flex enters to run. OC never reports DP as re-entering and she continues to pitch. Top of the sixth, DP gets another base hit. After the play is over, DC challenges the umpire that the DP never re-entered. What's the ruling and why?

[HugoTafurst]

NF rules:
F1 is the DP
F9 is the Flex

F1 gets a base hit in the top of the fourth. Flex enters to run. OC never reports DP as re-entering and she continues to pitch. Top of the sixth, DP gets another base hit. After the play is over, DC challenges the umpire that the DP never re-entered. What's the ruling and why?

F1 is an unreported substitute -
If this is the first time, team warning is issued, all play continues as if it was a properly reported substitute.
Next time, depending on your state, player and head coach are restricted to bench or ejected.