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 email@example.com 0 -remote- 7134 18.104.22.168 localdelivery domain.com 1 3.1 2014-12-03 05:19:07 1Xw9pe-0003aq-8b firstname.lastname@example.org 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.