We interpret this as too little milk in the frother.

If your Stelio milk frother (25cl) switches off after a short time and flashes blue/purple, there may be various reasons for this. Possible causes include an incorrect milk temperature, a defective milk nozzle, a displaced O-ring or even a fault in the appliance itself.

Check the milk temperature: Make sure that the milk is not too cold or too hot before frothing it.
Clean the milk nozzle(s): Clean the nozzle(s) thoroughly after each use.
Check the O-rings: Check that the O-rings are intact and replace them if necessary.
Check the amount of milk: Make sure you are using the correct amount of milk.
Try a different type of milk: If you try a different type of milk and the milk frother then works, the cause could be the milk itself.
If the problems persist, contact Stelio customer service.

We have never had this phenomenon before. So unfortunately I can't give any advice.
Hopefully your milk frother will be fine again soon!