Timestamp milliseconds not appearing

Hi there, I am extracting a timestamp in props.. everything is working fine except for the milliseconds at the end of it. Date format is 2017-07-11 08:54:12,815 -- my extraction is %Y-%m-%d %H-%M-%S,%3N That extraction works for similar data with a .(period) before the milliseconds instead of a comma - changing the end of the extract to .%3N - but it never works for a comma. Is there anything else needed when trying to extract milliseconds after a comma? Thanks