There is no direct way how you could ever convert CRYPT8 archives to CRYPT5 format, because they are of different version.
However, the WhatsApp Tri-Crypt program can be run as background process and convert all newer CRYPT8, CRYPT7 and CRYPT5 archives to the original legacy CRYPT format, which then can be easily extracted with one of the available tools like WhatApp Xtract.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
If you find entry that you feel is flagged as bad wrongly, please tell us in the discussion below with as much as information as possible so we can fix it.