I can’t see attachments in my Bitwarden app on iphone when I am out of range of cell or WiFi network. I use attachments to keep images of important documents that I may need when travelling abroad. But if my phone is not connected to Internet, even if vault is synched just prior to that, no matter what attachment I’m trying to download I get a message "Internet Connection Required’. This completely defeats the purpose of attachments in the first place and means that my local Vault instances are not fully synched. I was trying to find in the help section if there is any description on how attachments work in Flight mode, but could not find anything.
My understanding is that all attachments are stored in the cloud, on Bitwarden’s servers, and that your vault only contains links (URLs) that point to each attachment. I don’t believe that any attachments are downloaded to local storage when you download your vault on login, or when there is a sync. Thus, you would need an active internet connection to view or download any of your attachments.