Log Analytics is parsing but not recording

I have set up a CustomLog to automatically send traffic to Piwik

CustomLog "|/usr/bin/python /path/to//import_logs.py --url=http://myserver.com/piwik --idsite=1 --log-format-name=common_complete --output=/var/log/piwik/piwik-auto.log --debug --debug --debug --show-progress -" vhost_combined env=!dontlog

Obviously the path and URL have been changed to example versions.

In my piwik-auto.log file, I see this:

42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 42 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current) 43 lines parsed, 0 lines recorded, 0 records/sec (avg), 0 records/sec (current)

etc etc etc

So it seems to be parsing the logs, but never recording them. I don’t have any other error information as far as I can tell, so I have no idea why nothing is being recorded. If I run import_logs.py manually with a log file containing the same logs, it works fine.

Any help would be greatly appreciated, I have already been fighting this for hours.