The blue lights are a diagnostic which simply tell you how much water is flowing through each pump.
One pump flashing rapidly rapidly and the other solid blue is normal – both should be pumps running
One pump flashing and the flashing occasionally – both should be pumps running
Both pumps flashing rapidly is normal – both pumps should be running

Let me explain why you see what you see:-

Let me assume you have a thermostatic mixer shower set to 40 Deg C and you turn it on.
A mixer mixes hot water and cold water to get a water at temperature between hot and cold.
The mixer is cold. To get it to the right temperature the mixer valve cartridge opens the hot port so the hot water starts to flow through the pump on the hot feed. The flow exceeds 1.5 litres a minute and so the light on the hot pump stays solid blue for 2 seconds whilst the flow switch ignores the flow and then flashes rapidly.The hot SPB flow switch sends power to the hot and cold pump. Both pumps run. The flow on the hot increases because of the extra pressure so the hot still flashes
One pump is flashing rapidly rapidly and the other solid blue.

Hot water reaches the mixer.
The mixer starts to introduce more cold so the hot flow reduces.
The cold flow increases to a flow over 1.5 litres a minute.
Both pumps flashing rapidly.
The cold flow does not exceed 1.5 litres a minute.
One pump flashing rapidly rapidly and the other solid.
The cold flow is 1.5 litres a minute.
One pump flashing and the flashing occasionally

The SP22S needs a 4 way bridge.
The biggest problem we have with the SP22S the fitter has not used the 4 way cable bridge.
The second biggest problem we have with the SP22S is that after sending that wiring diagram the fitter still has not used the 4 way bridge. The third biggest problem is that having ignored the wiring diagram a second time they still wire it incorrectly.

This is how to wire up a SP22S