Mail message bodies disappearing after migrating to Catalina

I store my email messages on local/offline mailboxes in my Mail app. I run rules that when I receive a message through one of my IMAP accounts, it moves the message on an Inbox that is local on my computer. I then will manually move the message to a different mailbox based on the content.

I was on a 2014 MacBook Pro running Mojave, but recently migrated all my files to a touchbar MacBook Pro running Catalina. I migrated using a Time Machine backup, which included all of my saved emails.

Now, when a message comes in, it gets placed correctly into my local InBox mailbox. No problem reading the content. But after I move the message to the local mailbox relevent to its content (e.g. InBox --> Work --> Client1 --> Proposals), the message will appear in the mailbox, but when I open it, the message body is completely blank.

No matter what I do, I cannot recover the body info. Moving it back to the original local InBox doesn't restore the message, and neither does rebuilding any of the mailboxes (rebuilding, if anything, deletes the message entirely).

This is a known issue on the Internet, but I'm not seeing any movement from Apple to resolve this extremely important issue. Does anyone have any info on how to recover the missing info? I moved 50-60 important emails before being aware of this issue, and now I can't find the messages (or see any body text in those that I can find).

For reference, I've attached a Before and After screenshot illustrating the issue. The message came in on an IMAP server, and a Rule downloaded it and placed it in a specific local mailbox. I then manually moved it from it's original mailbox into one that is nested inside it. The original message is fully readable. The moved message is completely lacking its body info.