"13 days lost under AW 107" = 13 Days lost under Article of War #107. Usually indicates a penalty assessed by court martial or company punishment. Probably company punishment in this case (a company grade officer - Second Lieutenant through Captain - could only assess punishment up to 14 days). Probably a minor offense, like returning late from pass, a few hours unauthorized absence, fighting, etc. There would be a record but it would probably cost more to track down than it would be of interest.
Jennifer sent me a scan but I'm having a problem with my system. You can send it to my son at the e-mail I gave or send a hard copy to the physical I address I included.
I'm curious as to where you got this info on this "396th Whatever-It-Was". In addition to the other units I've mentioned there was a 396th Field Artillery Battalion and 396th Antiaircraft Artillery Battalion but neither were deployed in Italy. Send me his discharge (save wear and tear on both our keyboards).