Karn’s final ability is supposed to bring exiled supports back into the battlefield under your control. Multi0le times now I’ve had more than 20 artifact supports on the board before and activated it, but it only exiled the support tokens. All other supports stayed on the field and I received nothing back.
Hello @FindingHeart8,
Thank you for all the information provided, this issue will be investigated!
If you have any additional information that you consider relevant, please don’t hesitate to send me 
Rebeca