Adkins was left frustrated as his side failed to get going after a two-week break.
"It just didn't happen for us today," he said. "For me, it was uncharacteristically flat for whatever reason.
"Obviously I will digest that and with the goal we conceded just before half-time, there are two or three people that could have done better in stopping the goal.
"That has obviously given Sunderland something to hang onto in the second half and, to give them credit, they defended well.
"We tried to change things around early to give ourselves an opportunity to increase the tempo, find a way forward, stretch the game to create openings, but unfortunately we haven't scored any goals."