The SFC5 controller is designed to operate with a 12V pump max rated to 9 amps and up to around 7 - 10 LPM, For a larger rated pump I would suggest the High Current controllers which will operate pumps up to 30 amps and larger LPM rates.
In answer to the question the controller is cycling the pump in and out of DE. This is likely to be due to calibration setting being too low, Using auto cal can help, The video and user guide suggest setting flow to 30 as step one in auto cal, It does not have to be set to 30, I would suggest flow is set to what you expect to use the majority of the time
When the controller is calibrated to the pump what we are doing is telling the controller what base line current draw and pressure in the system is during open flow. When the tap is turned off both current and pressure increase, the controller detects this change and DE,s the pump.
On flow being restored current and pressure drop back to the normal open flow level and the pump restarted.
If calibration is to low and the pumps draws more current than the controller expects it may cycle in-out of DE, with a 9 amp rated pump increasing the calibration means the controller sees the high base line and less sensitive. Higher flow rates will mean Cal is also higher and the controller will be slower to DE the pump
If by chance the pump is a higher rated one for example 13 amps or perhaps has a higher LPM rate say 15LPM them I would suggest using a high current controller which are designed for these higher rated pumps.
With a higher LPM (EG 15) pump setting flow rate to 30 - 40 or so will have the pump producing 6 - 7 LPM at the output of the pump. Now depending on the hose ID this may exceed the maximum volume the hose can carry, in turn this can cause the pump to work harder which increases current and pressure, triggering the cycling
In some cases to give required flow volumes a larger ID hose on the reel or pole may help. Restrictions will impact flow rates particularly if the pump is producing a higher volume than the hose line can carry . The Hose it self can be a restriction due to expansion rate, temperature and hose wall stiffness.