4.20 Waits for IO forever when opening a level

Hello I am working on upgrading my 4.19 project to 4.20. Migration process is almost done and Windows build works very well. But when it packaged for Android, it stuck at opening level.

here is last few line of the log:

08-06 13:40:30.432 25501 25535 D UE4     :
08-06 13:40:30.432 25501 25535 D UE4     : [2018.08.06-04.40.30:432][  0]LogAndroidEvents: Display: DequeueAppEvent : 11, 0
08-06 13:40:30.460 25501 25535 D UE4     : LogGameMode: Display: Match State Changed from InProgress to LeavingMap
08-06 13:40:30.460 25501 25535 D UE4     :
08-06 13:40:30.460 25501 25535 D UE4     : [2018.08.06-04.40.30:460][  0]LogGameMode: Display: Match State Changed from InProgress to LeavingMap
08-06 13:40:30.460 25501 25535 D UE4     : [2018.08.06-04.40.30:460][  0]LogGameState: Match State Changed from InProgress to LeavingMap
08-06 13:40:30.461 25501 25535 D UE4     : [2018.08.06-04.40.30:461][  0]LogNet: Browse: /Game/Levels/Login
08-06 13:40:30.462 25501 25535 D UE4     : [2018.08.06-04.40.30:462][  0]LogLoad: LoadMap: /Game/Levels/Login
08-06 13:40:40.521 25501 25726 D UE4     : Waited for 10 seconds on IO....
08-06 13:40:50.523 25501 25726 D UE4     : Waited for 10 seconds on IO....
08-06 13:41:00.525 25501 25726 D UE4     : Waited for 10 seconds on IO....
08-06 13:41:04.269 25501 25501 D UE4     : Battery: status = 2, rawlevel = 35, scale = 100
08-06 13:41:04.269 25501 25501 D UE4     : nativeBatteryEvent(stat = 2, lvl = 35  temp = 33.00 캜)

it keep saying Waited for 10 seconds on IO.... forever but I can’t figure out what is loading at that moment. Is there any tips to resolve the situation?