At present, the release of SharpCompress that Serialization uses is missing the fix for single-block solid archive detection that was pushed a month or so afterwards adamhathcock/sharpcompress#924 . From my own observations, and the experiences of various MPF/BOS users, solid archives (especially solid 7Z archives) tend to only be one block, so this winds up being a pretty major issue, resulting in extraction more or less locking up anytime a 7z is encountered. I understand that this fix isn't the most elegant, but it doesn't actually waste that much time since it only needs to check for two file entries, and it will have a major positive impact on processing times, given the state of solid extraction without it is borderline unusable on large archives with many files.
This backports what I had done for the original commit SabreTools/BinaryObjectScanner@ecd99b1 in the pull where this was first found SabreTools/BinaryObjectScanner#375 .