Dear Andy,
In the past when I faced a similar problem (triggers did not always trigger), I changed the trigger to a 'Re-occurence' trigger. For example to run every 30min.
Then the flow would get all the files via a 'List items in folder' or something similar and compare the output with a central file of previously processed files. Files not in the list would get 'processed' further as per actions you decided.
You could even considered moving 'processed' files to a different folder.
I know this may be a bit more complicated than the 'Trigger when file created', but it should prevent you from missing anything in high volume.
Hope the suggestion helps,
Happy flowing,
Koen
