False alarms
Although the individual patterns that we use as triggers occur rarely in a process that is in control, they do occur occasionally. Indeed, the proportion of values from a stable process that triggers each of the criteria is typically about 1 in 200, so if all five criteria are used, a reasonable number of false alarms will occur.
Clearly a single exceptional value is not conclusive proof that the process is out of control. However it is appropriate to examine carefully the operation of the process to look for an assignable cause for this value (and adjust the process if such a cause is discovered). And a series of such values does indicate that the process is out of control.