See it the data is there

#echo  'select * from eximstats.sends limit 2;' | mysql
mailtime        msgid   email   processed       user    size    ip      auth    host    localsender     domain  spamscore
2014-12-09 21:38:11     1XyZyR-0004j1-5K        santa_2014@domain.com 0       -remote-        7134    37.48.84.200    localdelivery   domain.com    1               3.1
2014-12-03 05:19:07     1Xw9pe-0003aq-8b        mobileco@domain2.com    0       mobileco        3256    127.0.0.1       localuser       localhost       1     domain2.com  2.1

If data does exist (you can also check the other tables: defers, failures, smtp in the same way). If you get no data than for some reason data is not making it from exim into the database.

Check if an upgrade has failed.