Unable to send attachments in email tool

Our team received a ticket issue from an instructor unable to send pdfs through their email class list tool within D2L. Our team also recreated this issue in another course and with different PDF documents. Attached are the error messages we receive when trying to send multiple PDFs and a single PDF. We've confirmed that none of these documents either separate or together surpass the file size limit for Brightspace to send. Would someone be able to look into this issue and let us know why we are receiving this error message? Thank you!