Thanks for sharing these details. I think this is too specific to include in Converter reconfig; perhaps a KB will do...
As for the tar issue - I am 100% certain the helper VM tar (1.20) supports files larger than 4GB (it has been tested with files larger than 2TB) and 99.99% certain the source machine tar (1.15) also supports them. From your messages I am not sure whether you have ruled out the network error possibility. What I mean is retrying the conversion with the problem volumes. Perhaps you could try converting just one of those volumes if you want to test it.
If that is not a network error, honestly, I am short of ideas. If you can copy these volumes separately as a workaround, perhaps this could just remain a mystery.
Regards