https://sports.yahoo.com/nfl/article/nfl-standoff-why-30-of-32-second-round-picks-remain-unsigned-163741704.html
The sticking point is guaranteed contracts for second round players. The first two picks in the round have been granted fully guaranteed contracts. Now the remainder of the picks in the second round are holding up signing as they look for the same. This includes TJ Sanders for the Bills.
It will be a shame if Sanders misses camp over this issue s The Bills likely have him heavily penciled into their D-line rotation plans.