USPS delayed sending my mail to USCIS for H1B petition

My employer sent all the docs to USCIS through USPS on June 25th and it was expected to be delivered by June 28th 2021. But USPS unusually delayed it. No movement between June 30th till July 14th. Finally it was delivered on July 15th 2021. Now USCIS, denied it saying its too late.
Anyone ever faced it? My friends whose package was sent on June 28th too got accepted & received Recipt numbers for their cases. My employer is saying we can send letter to USCIS with proofs about USPS tracking history, but doing it very slowly.
Anyone has any idea about such situation? What can be done? Does USCIS consider if we give proofs?

Have your attorney submit the proof, hopefully USCIS may consider it and process your application.