If your inventory is full, and you are trying to gather more of something you already have from the storage locker, the action will fail.

For example, if you have 2 plants in hand with all the other inventory slots filled, and try to collect one more plant from your storage, it will fail.

You can still push the two plants into the locker (because the locker isn't full?), combining it to 3 plants total, and then take them back into your personal inventory.