Upon OLT reboot, OLT's OPERSTATUS is observed as "rebooted" and no ONTs are discovered

Customer DT reported:
Upon successful OLT reboot, the OPERSTATUS in VOLTHA CLI is observed as "rebooted" and remains in that state. Also no ONTs are discovered. This is not the expected behavior. The issue reported here is even after waiting for long time (more than 15-20 mins) , the state of the OLT remained in rebooted state and hence no ONTs were discovered.

Expectation is that the state of the device shouldn't stay in "rebooted" state for long, after clearing up all the ONTs and resources, Adtran adapter has to move the state to reachable and the ONTs should start getting discovered.