I got an update from the product team. There are two different FWs for MR5100-1Z1MES units. The FW v10.x.x.x is the latest FW for MR5100 units with 4GB of memory. And the customer with 8GB of memory MR5100 can only update to FW v12.04.12.01.
As for the issues with the FW 10.x.x.x, kindly report those issues to Zain for them to check.