I too am having the same problems of looping at 90.90% at 99985677.
Used: reaver -i mon0 -b MAC --dh-small -vv --delay=0 --recurring-delay=30:15 --no-nacks
Works beautifully (?) at this point until it reaches 9985677; then it just keeps looping. Changing to -pin equals 99985678 does not seem to help.
AP is a Belkin router. My laptop using BK5r3 and 1.4 Reaver. Dell network card 1450 (?); been able to crack several other APs without any unusual problems; some very quickly. I've tried all the channel IWCONFIG and AIREPLAY-NG suggestions on numerous threads but nothing seems to tackle the loop on this specific number. Anyone with any ideas??