There are some instances such as virus was not get detected after scanning the server using the ClamAV scan engine. This was due to lack of definition regarding the infection on the database. In such cases which has an identified threat but not detecting, you can directly report to the ClamAV online reporting portal.
ClamAV: https://www.clamav.net/reports/malware
Once the instance was addressed ClamAV will add the necessary info to the database which will be updated to the server while updating the virus definition database. This helps to detect the infected file on the server which was excluded from the last scan