hi Francis,
This small modification will give the required result for flashing and breathing.
The breathing LED brilliance range is limited but it will give you an idea.
AA1 image is flashing and AA2 image is breathing

E

 

Rookies frequently mistake "noise" as coming in from afar.
While not seeing the hash they generate themselves.
Decoupling caps are ice cubes: you notice them by their absence.

In software it's "watchdog resets": rare to have too many, trouble if too few.
I got the scars... L8R <<<)))

 

An old fashioned 555 and 556 use TTL logic from the '70ies. When its output switches it causes a 400mA current spike on the power supply so decoupling is important. Maybe your power supply cannot produce this required 400mA plus the LED current?

A Cmos 555 and 556 do not have this supply current spike but their amount of output current is limited.