Air carrier Cargo Load Crew Chief reported undeclared Hazmat cargo transported. The cause was a communications breakdown between Load Crew Chief and loading crew which was discovered after aircraft departure.

Narrative

On Date; approximately XA00; I was given a task on [Rover] to load an outbound Aircraft X to ZZZZ on Gate X for a XB:50 departure. I entered the gatehouse and began to print and review the load plan sheet assigned by the planner. Looking to assign the crew in the most efficient and productive way; I assembled the crew and communicated my expectations on how I planned to complete the task. They all grasped my approach and initiated the plan as I described. They connected the pin; towbar; and huff. We opened up both forward and aft compartment doors; and strategically placed a Widebody loader on each door to maximize the utilization and performance of my crew. I went outside to my tug; unzipped the orange crew chief bag and retrieved my scanner. I signed into the [name] app. I entered my user ID; password; and clicked 'log in' on the bottom of the screen. I then selected the app and clicked on 'initialize flight'. I manually entered the flight number; verified the date; and checked the small box 'crew chief flight' prior to clicking on 'initiate flight'. Three squares down on the right; I clicked on 'load'. While they performed that task; I began to take inventory of the LD3 [cargo] containers that were already delivered at the gate. Upon completion; I instructed my crew to commence loading the containers that were already at the gate as per the load plan provided by the load planner. As the LD3 containers kept arriving; I checked them off the list and made notations on the positions where I was loading onboard simultaneously entering it on the app. I instructed my crew to load a string of four (4) LD3's and went inside the gatehouse to print the NOTOC (Dangerous Goods Form) aka DG paperwork. Upon completion; I went upstairs and delivered the paperwork to the Captain. When I returned to my crew; I instructed them to close both doors and prepare for departure. At this point I realize I did not have the LD3 container; [Airways Bill number]; which contained the NOTOC; nor the container [Airways Bill number] with freight. I removed them from the load plan and finalized the flight. When my crew returned from pushing out the aircraft; we regrouped. That's when I realized both cans were indeed loaded. I quickly tried to contact load control to have them rectify the paperwork; but they stated they were between shifts and could not assist. I requested them to contact the Captain but again they stated the flight was in the air and could not reopen a flight after the aircraft takes off. I then contacted my Customer Service Manager as I was all out of options.I realized the event when my crew returned from pushing out the aircraft and we regrouped. That's when I realized both cans were indeed loaded. The event took place when I left my crew unattended continuing to load the LD3 containers while I went inside the gatehouse to print the NOTOC paperwork necessary to deliver to the pilot.I called and notified to contact load control to have them rectify the paperwork; but they stated they were between shifts and could not assist. I requested them to contact the Captain but again they stated the flight was in the air and could not reopen a flight after the aircraft takes off. I then contacted my CSM as I was all out of options with the weight discrepancy. My suggestion is to load one belly at a time thus allowing the crew chief to have more control of the aircraft. Preventing these types of abnormalities ... Lastly; longer ground times could prevent the need to rush to load both compartments simultaneously which will reduces the stress level on all parties and give us enough times to double check our weight and balances.