Hey Mogli,
I’m sorry about that. What I do is I usually test-run my experiments so I can spot this kind of problems.
There could be several explanations. The easiest for me would be if you shared your script or the link to your experiment with me.
How was your group distribution method? Did you rely on the internal counter? Or did you force a group assignment as a parameter in the URL?
When relying on the internal counter, and in absence of explicit manipulation in the script, if all your participants take the experiment within seconds/minutes, they could very well all end up in the same group (because the counter is only incremented when participants have completed the whole experiment).
Jeremy