Hi everyone - thanks for your patience. We understand how annoying this must be, and we're trying to get it fixed as soon as possible. 
We've had an update from the tech team, and they will be doing a release, which should hopefully resolve the problem, on Monday. Sometimes the small tech fixes can take a lot of work behind the scenes, but rest assured we're making progress with this.
They've also said that for now it looks like the messages are sending on the first click but it just isn't telling you that it's sent. In the meantime, you can click send and then look at your sent messages to check it's gone.
We hope this helps, and we will let you know if the fix has worked on Monday! 