Hello @Ariel Daza
we have encountered the same issue with Outlook 2019 and also confirmed it needs these three conditions:
- The sender name is a single string without spaces, e.g. "JohnDoe"
- The message subject contains a Re: or FW: prefix
- The "Show as Conversation" view is not enabled in Outlook
This can be reproduced with Edge and also Chrome browser.
We found that enabling the "Show as Conversation" view in Outlook could help as a workaround, as it's changing the subject to the conversation topic which doesn't have Re: or Fw: prefix. Then the drag & drop works. We opened a case with Microsoft to see what they can find.
Cheers