Resolving current location does not work
Although this is not a deal breaker, it is certainly an inconvenience. Having the app automatically determine the current location to select the source or destination of traveling makes dealing with the app significantly faster.
Sent an email to the customer support.
The customer support responded with the following message (original in German, translated to English):
Dear Mr Betschart
Thank you very much for your inquiry.
We support only SBB Mobile app versions downloaded using the official Google PlayStore (Android) or App Store (iOS). For any other sources we don't provide any guarantees. Alternatives are not planned.