Sorry to hear that. Please close Ava (go to your different open tabs and swipe Ava off) and start it again to see if you are now able to connect. Also, try to connect in multiple ways (from you to the participant and from the participant to you).
If this doesn't work, we would highly appreciate it if you would report this issue to us. You can do this in the app (swipe to the right and tap on 'Help / Feedback' to directly reach out to an Ava team member. The more information you'll provide us with, the better we will be able to solve the issue for you!