I dropped the single message that contained the message length error that contained the ping/response and re-ran the import job successfully! So I’m guessing the characters used within the message somehow are consuming enough characters above the predefined limit mentioned earlier (since the message character length was only 9432) as I did not encounter any additional errors after that point.
Thank you for your invaluable support and communication in order to get this finished! I’m not really sure which to mark as the solution since it appears to be a team effort.