Spark: blinking cyan when flashing from WEB IDE

Got a problem with “Spark Core” device. When I flash it from WEB IDE it goes fast blinking cyan forever - 3-4 yellow/orange slow blinks, sometimes white for a while. This cycle can repeat for very long time.
Resetting device to default firmware - works perfectly connecting from first attempt. Anything from WEB IDE (even basic blink a led code) - fails.
This happens on 0.5.* and 0.4.* firmware , choosing 0.3.4 looks to behave stable.
particle update cli command gives There are currently no system firmware updates available for this device.

What can I do to fix my device to work with recent WEB IDE code?

UPD: This looks like a solution Photon flashing cyan and blinking orange

UPD: After reboot core fails again, so that’s not a solution
@ScruffR any advice?