The last 3 games his snap counts have nose dived. Undisclosed nagging injury IMO. I don't buy into conspiracy theories of a haha we don't need you type of thing. They aren't going to do that to a captain of a football team. Diggs body language also does not support this as he is constantly hyping the team. You can see on film Diggs taking himself out sometimes.
I also think some of it might be the Bills trying to on the fly become "multiple on offense." I think they want to have more answers than Diggs because they need to. You can't rely on just one receiver to be the whole offense. So, they are working on that as the season goes on. Part of the reason why Dorsey was fired was he wasn't getting this done.