There was an hidden race condition in the Tuned code since the beginning of the Tuned v2 development.
If the switch profile command was sent to the Tuned daemon quickly more times (e.g. twice) and the previous switch profile command wasn't yet finished, the race condition may occur and the deadlock may trigger. In the deadlocked state the Tuned daemon stopped responding to further commands and had to be killed by the operator.
The Tuned code was modified for the deadlock not to occur any more.
Multiple quick requests can be processed now and the Tuned daemon still responds.