In the Sandstorm UI, if you go to "Apps" and choose the app, you'll see a "report issue" link in the upper-right. Generally, these link to the GitHub issue tracker for the app or its Sandstorm packaging.
I found a way to get to the github page of the app.
Added the issue there.
(Open the app in the app store and click on the '</>' icon to go to the github page of the app)
Maybe feedback and bug reporting could be built into the Sandstorm system in a user friendly way, without need for a github account, both for apps and Sandstorm itself?
The email app Roundcube does not seem to support unicode characters in the senders name in received emails.
So the displayed name in received emails gets garbled if it contains e.g. a swedish character like 'å', 'ä', 'ö'.