This can happen from time to time with an accident OR build up of traffic or you have three lorries abreast being complete .........!!!!!!!
Either direction sb or nb come off for the A414 St Albans if going South, A414 Hemel Hempstead if going North and stay far right and follow the road till you see the signs for the M1 again...This will allow you to bypass the build up of traffic and save you some time.