A timed out call to xapi would trigger that alert. The default timeout is 10 seconds. Are there any automated jobs that run on a regular basis that could cause xapi responses to be slow?
Also, if the slave is triggering the alert, it could be that the slave momentarily lost access to the master's management interface.
If its the master, you can try to increase the default timeout (10 seconds) to something slightly higher, but do not recommend making this value too high. This would merely silence an underlying problem.