Stress Test API - Ramp up settings and execution issues
Thank you Alex!
If you add to your test more concurrent virtual users than your license supports, LoadUI puts the “extra” virtual users in a queue and simulates them only if the license allows. If you experience this behavior, consider upgrading your license to another one that supports a greater number of simultaneous virtual users.
And, this article might be of interest as well, it speaks of Stress Testing:
Creating stress tests usually requires more virtual users than it is available for the Base (Free) LoadUI license. So, you need a LoadUI Pro license.