Search /home/awstats/DirData/ for any files relating to the domain you’re dealing with and are newer than those for which you have logs.
eg…
ll /home/awstats/DirData/awstats*.www.example.com.txt
ll /home/awstats/DirData/awstats*2015.www.example.com.txt
and then either remove them (if you know you can recreate them) or move them to a temp location
rm /home/awstats/DirData/awstats122015.www.example.com.txt
mv /home/awstats/DirData/awstats*.www.example.com.txt /tmp/awstats.tmp/
Unzip all your log files
cd /log/directory/
gunzip access.log.*
/usr/local/www/awstats/tools/logresolvemerge.pl access.log.* > access-history.log
gzip access.log.*
Edit your /usr/local/etc/awstats/awstats.www.example.com.conf file and point LogFile to access-history.log
Run awstats_updateall
/usr/local/www/awstats/tools/awstats_updateall.pl now -configdir=/usr/local/etc/awstats/
Check stats are now as you expect
https://www.example.com/awstats/awstats.pl
Edit your /usr/local/etc/awstats/awstats.www.example.com.conf file and point LogFile to access.log again
Run awstats_updateall to get most recent data
/usr/local/www/awstats/tools/awstats_updateall.pl now -configdir=/usr/local/etc/awstats/
Check stats are now as you expect
https://www.example.com/awstats/awstats.pl
Delete access-history.log