Are these ladder-logic "PID" instructions or function block diagram "PIDE" instructions ? I'm going to guess it's a ladder-logic PID.
Are there any timers, subroutines, or other methods being used to make the PID instruction execute periodically, or does it execute every single scan of the PLC ?
The ladder-logic PID requires both that you tell it what the update time is (the Loop Update Time field on the Configuration tab for the instruction), and that you execute the instruction at that rate.
Placing the PID instruction in an unconditional rung in a routine that is executed by a Periodic Task is the most precise way to guarantee execution at a periodic rate.
But it is also possible to get good performance, especially with relatively slow PID loops, by executing a subroutine containing the PID instruction based on a timer, or some other timing method.
If your PID instructions were executed at a rate equal to the PID Loop Update Time field, then you can move them to a periodic task without re-tuning them.
If they were not executed at a rate equal to the PID Loop Update Time field, then they will need to be re-tuned if you change their execution rate.