What are the scenarios in which it can happen and possible reason behind that?
May vary by very few decimals for farther month contracts,as you are asking for near month it is safe to assume delta as 1, at least for index futures. It can depend on carrying costs also but for a retail perspective one can ignore those to avoid further complications. Also as we come close to expiry delta gets closer and closer to 1.
I observed few near futures contract moving slower compared to spot which has put me in a state of confusion, I correctly remember it was moving like 0.5-0.8 compared to spot.