locust-plugins: "Failed to reach target rps, even after rampup has finished" with limited load

I’m running a simple script with a task like that:

def mytask(self):
	self.rps_sleep(self.rps)
	jObs = {
		...
	}
	head = {'content-type': 'application/json'}
	self.client.request('POST', '/api/observations', data=json.dumps(jObs), headers=head)

and even with 2 clients and an rps of 1 I’m getting “Failed to reach target rps, even after rampup has finished” as soon as I run locust. Any clue?