The bug is in my opinion related to his very strange contract history. He was signed to a $5M/yr x 4 yr contract in season 45, and then waived later in the season; my guess is that he was accidentally placed on irrevocable waivers rather than revocable waivers after the trade deadline, and the owner got stuck with no way to assign him. He was released by the AI after 10 real days on waivers. At this point, any team could have signed him for $327K, and somewhere in the code this fact had to be recorded.
However, no one did-- and his previous team re-signed him at the beginning of season 46. This should have reset his salary to the original contract, and it appears that in the "contract" part of the code it did that. But I'm guessing that the $327K is still being read by the Rule 5 code as the salary you have to pay him. It isn't, of course; the $5M is correct. But you set yourself not to draft that salary. The Rule 5 code is bugged.
Send a ticket. Assuming you got your settings correct, the Rule 5 claim should be revoked.