Hello Stephan,
Good Afternoon. Let me start by telling you how this happens.
Imagine that Survey 1 is scheduled to be prompted at 11 PM and expires 55 minutes later. It is also scheduled to be prompted at 11:49 PM. So at 11 PM, a session will be created for Survey 1, and participants will be prompted to respond to it. This session will stay open until answered, or until 11:55 PM.
In the meantime, a new session will be created for Survey 1 at 11:49 PM. Keep in mind that Ethica only allows one open session at a time. So if Survey 1 is not answered and its session is not closed before 11:49, the next session will immediately close after opening and it will not be prompted to participants. In other words, the 11 PM session blocks the 11:49 PM session.
Having said that, to keep this from happening, you need to make sure that your participants complete a session before moving on to another session.
If you still get the same problem, please let us know.
Best,
Aso