Update: I managed to find the following in the ORs, so at least I know it was the brigades of Finegan and Harris of Mahone's Division:

• OR XLII, P2, page 770: John C. Babcock to Humphreys. September 10, 1864:
GENERAL: Five deserters and fifty-seven prisoners of war were forwarded this a. m. from General Mott’s Division, Second Army Corps. The deserters are all from the Eleventh Florida, Finegan’s brigade, and came into our lines shortly after dark last evening, just previous to the capture of the prisoners. The prisoners represent two brigades of Mahone’s division, Finegan’s and Harris’. Ten of them are from the Twelfth, Nineteenth, and Forty-Eighth Mississippi, of Harris’ brigade, and the remainder from all the regiments of Finegan’s brigade. The picket-line of Harris’ brigade was attacked by us near its left where it joins Finegan. Harris’ Brigade lies to the right of Finegan. None of the deserters or prisoners give any information of importance. The position of Hill’s corps remains unchanged. Some of them report a division of Longstreet in rear of Mahone; suppose it to be Field’s division. More than half of Finegan’s men seem anxious to take the oath of allegiance and go North.

• OR XLII, P2, page 770: John C. Babcock to Humphreys. September 10, 1864:
GENERAL: Twenty-four prisoners of war from the Twelfth, Sixteenth, and Nineteenth Mississippi have been forwarded from the Second Army Corps in addition to those received early this a. m. The total number received this far is eighty-three, representing only Harris’ and Finegan’s brigades. The last bring no additional information.