Not sure why but using Mekanism pipes, the drawers seem to go to 512 and then Mekanism pipes wont import anything else into the controller even if the item is already in the pipe.

forge-32.0.108
StorageDrawers-1.16.2-8.1.0.jar
Mekanism-1.16.1-10.0.9.432.jar

Still happening to me with StorageDrawers-1.16.3-8.3.0.jar

Just a heads up, Hoppers dont seem to have this issue.

Just tried doing the same with hoppers and it works fine, maybe Mekanism?

See #811 , this sort of thing has been going on for some time.