Why did the apostles have a hard time recognizing Christ each time they saw him after the resurection?
Jesus Christ was the first fruits of the resurrection. Before that, there was really nothing to compare. On that first Easter morning, Mary entered the dark tomb with spices to anoint Jesus’ body. The sorrows she felt over his death were only compounded when she found the tomb looted and his body missing. Teary-eyed, she turns to leave and sees a silhouette blocking the morning light from the entrance. Given her emotional state, as well as the physical conditions of the tomb that morning, it is fully understandable that she did not recognize Jesus until he said her name (John 20:14-17*).
When the Apostles first see the resurrected Jesus, it doesn’t sound like there was any confusion on who it was. They were “terrified” because they “supposed that they had seen a spirit” (Luke 24:36-49*). They recognized the man before them as the same corpse recently lain in a tomb. The evidence laid before them was of the corporeal body (eating and being handled) rather than proof of identity. After they got over their initial shock, the Apostles were “glad, when they saw the Lord” (John 20:19-23*).
On one other occasion Peter, James, John, Thomas, and Nathanael were out fishing when the resurrected Jesus greeted them from the shore. This time he went unrecognized until he performed a miracle similar to when he first called them. He may have initially been unknown to them because of the distance (close enough that they could hear him, but perhaps far enough that they couldn’t tell him apart from other persons), and also the orientation of the sun (the miracle happened when “the morning was now come” (John 20:19-23*).
One final example is the two disciples on the road to Emmaus. This one stands out from all the others because he still remains unknown even after a lengthy dialogue. The scriptures do not say how well these two disciples knew the Lord, or if they were among the many converts brought to the faith through the Apostles. Presumably, they had worked with Jesus previously (after talking about Peter and John visiting the tomb, Luke mentions two “of them” as though they are among the leadership). Luke shares why they didn’t recognize Jesus, “their eyes were holden that they should not know him” (Luke 24:13-32*).
So when it comes to the witnesses of the resurrection, most recognized Jesus and were glad to see him alive, a few struggled with the physical conditions obscuring his identity, and some had their eyes held in check and restrained.