A customer has reported a bug that neither them nor us have been able to reproduce. This is the only report of this bug happening so far.
We've spent a lot of time trying to replicate the issue (followed the customers' exact path, with their same browser, and even set the server and local machine clock to replicate the time the bug occurred).
Given that we can't fix a bug we can't get to happen again - how should we proceed? Should we log the bug and wait to see if it happens again or is it critical that we not move on until it is reproduced? What point is it acceptable to "cut our losses" with finding the problem? What should be communicated to the customer?
Thank you all for your advise!