Emojis disappeared during a send, $wpdb charset showing an error

Hi,
I have a newsletter that goes out ~monthly to 40K subscribers and takes 2-3 weeks to run. This last issue started delivery and all emojis showed up fine. The most recent deliveries of the same newsletter now have errors (? instead of emoji and ? instead of apostrophe).

Also, in the list of newsletters, some completed newsletters no longer show the subject – it is just blank. The newsletters that show a blank subject had a subject line that included a ™ character. The newsletter was paused over weekends, I don’t know if the error happened right after a send restart, or how it corresponds to any recent updates. The problem is affecting newsletters that were previously sent as well as the current sending one, if I pull up an old sent newsletter in the app – all of the apostrophes are now ?, etc.

In digging through settings, I did find the following flag in Help-System-Database:
$wpdb charset – Charset: latin1 The recommended charset for your database is utf8mb4 to avoid possible saving errors when you use emoji. Read the WordPress Codex conversion instructions (skilled technicia required).

Let me know if you need further information.