Shimano's instructions also call out a specific (low) torque for the NDS cap in order to preload the bearings and seals correctly. Too much and the seals open a little to let dirt and water in and then the bearings fail. That's probably the weakest aspect of HT2 and often overlooked. Newer HT2 BBs may have better seals, but still, follow the instructions.

And make sure the NDS arm slides easily on the splines during preload.