I have just purchased a kit of 3 Deco S1900

They are set up as access points, with one being set as the 'main' one but they're all wired back to the main router (possibly via an ethernet switch).

They've worked well for a few days but I noticed the 2 'satellite' ones have started blinking red, while the 'main' one has the solid white light.

I still have excellent coverage around the house and the app is showing 'no issue', so why are those 2 blinking red?