Hi info1782,
The "archive is corrupted" error simply means that the scan could not unpack the archive file, not that the file is corrupted. This most often happens when a proprietary file compression system is being used.
The "The file is a decompression bomb" error does not usually mean that the file actually is a decompression bomb (
https://en.wikipedia.org/wiki/Zip_bomb). Typically, this error occurs with heavily compressed files as they can bear some resemblance to a decompression bomb. As a compression bomb works by overloading the system when it is unpacked, the Avast scan does not unpack these files simply as a precaution.
If there was something malicious embedded inside the compressed files, it will be identified if/when the file is unpacked by another program (as the File Shield will scan any compressed file at the time that it is unpacked). Therefore, it is safe to ignore these "unable to scan" results.