Automation to flash the lights

Let me guess, you’re using Device as an action instead of Perform Action, right?

Device actions are quite limited when compared to perform action calls.
All possible Device actions for a light:

type: turn_on
device_id: c6aa2d4414274e86f99490641a7cad8b
entity_id: 2ff5e4cc37a1a0e34df4bc2eced02f51
domain: light
flash: long
brightness_pct: 17

vs all possible Perform Action actions for the same light:

action: light.turn_on
metadata: {}
data:
  transition: 29
  brightness_pct: 17
  effect: blink
  color_name: blue
  color_temp: 180
  brightness: 63
  flash: long
  color_temp_kelvin: 2828
target:
  entity_id: light.kitchen_strip

Yes, you can use a repeat_while/ repeat_until to do that (docs here). Just make sure you add a suitable delay in between each loop, otherwise you’ll flood your system with constant light.turn_on commands.