trac-admin repository sync/resync randomly stops syncing

[adf@…]

There are 36868 revisions in my repo.

I am trying to sync the repo after adding it, it stopped doing it after a few hundred, then after a few thousand, then it did around 22,000 and stopped, then on running again, just stoped at same point, then run again, carried on.

[root@svnmirror ~]# trac-admin /var/trac repository sync INFORMATE
Resyncing repository history for INFORMATE... 
23281 revisions cached.
Done.
[root@svnmirror ~]# trac-admin /var/trac repository sync INFORMATE
Resyncing repository history for INFORMATE... 
23281 revisions cached.
Done.

Then started again, processing revision 24240 …

[root@svnmirror ~]# trac-admin /var/trac repository sync INFORMATE
Resyncing repository history for INFORMATE... 
 [24240]

and stopped.

[root@svnmirror ~]# trac-admin /var/trac repository sync INFORMATE
Resyncing repository history for INFORMATE... 
2539 revisions cached.
Done.

Started again, but this time, its processing revision 1536??

[root@svnmirror ~]# trac-admin /var/trac repository sync INFORMATE
Resyncing repository history for INFORMATE... 
 [1536]

If I look in trac, it shows the last revision as 36868 but shows no information for those revisions.

No errors are reported, so not sure what's going on.

The server is running in a VM. CentOS 6.5 and using sqlite as the database.

There are multiple repositories configured but not all have been synchronised yet. The DB is around 120MB currently.