Try clearing out your browser's cache/browsing history. When you have done that, close out the browser and re-start it in a fresh session. If that doesn't do it, then try using a different browser. If it persists, call Comcast security and have them look at your account---------------------
Comcast Customer Security Assurance-------------------
Normal business hours (6:00 am to 2:00 am EST, 7 days a week)
1 - 888-565-4329
FWIW, the following post describes a similar issue:
Random read receipt requests when sending email via Comcast webmail 02-13-2020
Issue: Editing a draft email (even if it is only in order to send it) triggers the addition of a read receipt request.
Workaround: If you have edited a draft email (from your "Drafts" folder), don't send the email from that window. Instead, create a new compose window, copy the addresses, subject, and text of the email from the draft window to the new compose window and send it from there.