Using Classic Outlook on Windows for personal email, calendar, and contact management
Having the same issue reported last week with one and we've updated the Monthly Enterprise Channel to Office Version 16.0.13530.20528 and I now have another one. They are using the work around of changing the message to rich text. The main mailbox that's doing the reply is already cached on both of the clients affected. Can use webmail to get around it but it's not a solution. Something's been broken on the client as this wasn't a problem till the last 2 client drops for us.