We've come across an issue with the module storage that can affect CMDRs when unique modules are stacked onto a ship. Firstly, PLEASE DO NOT do this as the outcome is a Commander Data error. This will mean you'll be unable to load the Commander!
If you move a unique module from your storage (Shield Gen, D.Scanners, and others that you can only fit one of) into a ship that already has another module of that type in a different class slot, this is when the issue will occur. For example, moving a Class 7 Shield Generator from storage when the ship already has a Class 5.
If this is something that you've experienced and you're unable to access the game because of it, please contact our Support team with as much detail as you can provide so that they can resolve the issue for you. The dev team are working on a fix and we'll resolve this issue ASAP.