Missing some attachments after migrating from 1PW 7 standalone to 1PW 8 (mac + iOS)

After using 1PW standalone with vaults locally + on different servers I finally took the bait and upgraded to 8. However by sheer randomness I found out that some attachments (typically mail messages) did not migrated while others did. Is this a known bug? It feels that the migration process can not be trusted, which is somewhat frightening considering the data 1PW is made for.

Am I alone in this? Any suggestions?

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1Password Version: 8.8.0
Extension Version: n/a
OS Version: macOS 12.5.1
Browser:_ n/a