Distributed Jmeter max number of servers
Theoretical maximum value of slaves is very high, you can have as many as 2 147 483 647 slaves which is a little bit more than 5.
So my expectation is that the problem is somewhere else, i.e. there is a maximum number of connections per IP defined or the broker is running out of resources
We cannot give meaningful advices unless we have more details, in the meantime you can check:
- jmeter.log files for master and slaves
- response data
- kafka logs
- resource consumption on kafka broker(s) side, it can be done using i.e. JMeter PerfMon Plugin