the problem could be that you included a 2018 addendum (whatever that is) with the 2019 return. It should have been sent separately. Or it could be simply that the IRS for 2-3 months wasn't processing mailed-in returns. It is thus far behind in processing them so it just might be that the IRS hasn't gotten to your return yet. There is no way to know for sure what's happening with your return.
the problem is that if the IRS got your return and you send in another copy it could further delay processing.
another issue with sending in another set, again 2018 should be sent separate from 2019, is that if the IRS got the first filing and you send in a second, the IRS will likely cash both checks.
I suggest waiting until at least the end of August before doing sending in a second set. after that, it's up to you to decide whether to wait further or submit a second set. This time use a method where you get proof of delivery.
