I've experienced that/similar issue this week. I reset my phone and I think that helped.
The issue was occurring (for me) when I was clicking on a link via (Yahoo) email and then being forwarded to the eBay mobile website. I was responding to buyers but the messages weren't showing as sent (until I reset my phone), and sometimes I'd click on the link to contact customer and would automatically get forwarded to a page saying, email sent, when I hadn't typed anything. Quite confusing.
Try resetting your phone and if that doesn't work goto your phone settings and clear all user data (you can also clear cache if you want), then reset the phone again and restart the app.
