In the Hyperlinks panel, Email hyperlinks that include a subject that includes an ampersand will change from an Email-type to a URL-type when you click OK. Status will then appear as a red dot in the Hyperlinks panel instead of an envelope. Opening it again from the Hyperlinks panel will show the subject gone and in a URL format.

TO TEST - Highlight text in your document. Open the Hyperlinks Panel. Create a new hyperlink with the [+] button at the bottom of the panel, choose email as the type, type a valid email address, then enter a subject line that include an ampersand (&) . Click OK.

THE FIX - Removing the ampersand from the subject line will keep the issue from occurring.