I have previously activated Secure2u on the MAE app on my current device. I have since uninstalled MAE and only recently downloaded it again on the same device. Do I need to activate Secure2u again?

Yes, you will need to activate Secure2 again. However, you do not need to wait for the min. 12-hour activation period to start approving transactions as you have previously activated Secure2u on the MAE app on the same device.