It may be because the CRUSH map has been changing very fast and the OSDs have fallen behind. To recover do this:
ceph osd set noup
ceph osd set nodown
ceph osd set noout
Start all the OSDs and when they are all showing the same or <1000 epoch value:
for OSD in {0..9}; do ceph daemon osd.$OSD status; done
ceph osd unset noup
Once the cluster is recovered:
ceph osd unset nodown
ceph osd unset noout