Your backup will work properly despite this warning
The ZIP format is by design very resource intensive and may cause your backup to fail, especially if you have a slow host and/or big files.
As per the ZIP standard, Akeeba Backup / Akeeba Solo has to calculate the CRC32 hash (a "signature") for each file stored in the ZIP archive. In order to do that, it has to read the entire file and run a processor-intensive algorithm. When combined with a large file and a slow host, this will most probably lead to a timeout. However, this is unlikely to happen and your backup will work properly under most circumstances.
If you are in doubt, you can always use the "JPA Format" which is a much less resource intensive archive format, developed especially for use with Akeeba Backup / Akeeba Solo.