Is a double tap acceptable on a main ground lug? One ground wire was for the main panel and the other for a 100 amp sub panel. Is there any information that covers this from the NEC?
Also, I am familiar with Square D QO breakers but I believe this one is double tapped?
Should not be two conductors. And hard to tell, but the one with multi-strand conductor looks like maybe some some strands are cut… but difficult to tell for sure.
As stated by others a code violation, the code reference is in Kenneth’s link in post #3. Just my 2 cents, when possible for clarity try to avoid using the term ground wire which is too ambiguous to really explain the conductor’s function. In the photo you have a black wire with a white stripe which is more likely to be a grounded or neutral conductor.