On Ph3, this typically means Ambarella is restarting.
This can be checked by connecting to UART.
Oh, also - sometimes it's just because of SD-card, and removing the card makes Ambarella work.
Ambarella is a chip which controls both SD-card and the LED. It drives CMOS sensor, gets image data from it, and sends to SD-card, while also preparing lower quality video for FPV. That FPV video then goes to DaVinci which is compressing it for radio transmission.
EDIT: Somehow I assumed the question is about gimbal light. So the answer above is for that - if you see such sequence in gimbal LED, not arm LEDs.
Update: I was getting those light sequences in my back yard and in the local park(West Ham Park, London). I tries in a larger park(Victoria Park, London)and even though an app I use showers a similar number of satellites available it now just flashes green! I guess there must have been some interference that isn’t there in a larger open area.