Chad Coleman
I found a solution to this problem. Someone on Twitter reached out to me with a fix. Turns out even if you're not planning to use them, you have to enable the gmail IMAP folders set to "Show in IMAP" for Sent, Drafts, All Mail, Spam, and Trash. You can uncheck Starred, Snoozed, and Important. Open Mail on your Mac and then Synchronize your account. The Sent items should appear again. Very weird that this works and doesn't explain why it doesn't affect other gmail accounts, but alas.