entryCSN is larger (later) in consumer node than in provider node

All,

I am having a out-of sync situation now with some entries' entryCSN is larger (later) in consumer node than in provider node. So the consumer never gets updated since it thinks it has the latest value.

provider: entryCSN: 20160520164908.960158Z#000000#001#000000

consumer: entryCSN: 20160521191401.646572Z#000000#000#000000

slapd.conf in consumer:

overlay syncprov syncprov-checkpoint 100 10 syncprov-sessionlog 100 syncrepl rid=003 provider=ldap://server.u.edu bindmethod=simple binddn="cn=Manager,dc=u,dc=com" credentials=password searchbase="dc=u,dc=com" schemachecking=on type=refreshAndPersist retry="60 +"

Any hint about this? Thanks a lot!

Frank