Messages that are sent without titles cannot be opened. The link to open a message is applied to the message's title, and if the title is blank there obviously isn't a link to click.
Messages that are unread have a bullet point next to the blank title which can be clicked. Therefore, new messages with blank titles can be read. To re-read a previously opened message that has no title, mark it as unread to bring back the clickable bullet point.
Two possibilities. Firstly, make it impossible to create a message without a title. This is the best solution. Alternatively, make the body text excerpt also a link, or add a "read" button next to the title somewhere.