One of possible reasons is that there is not enough voltage provided by the grid.
Unpredictable wind from wind farms, more and more fast chargers for electric vehicles.
It could be earth changes too or multiple factors at once.
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According to this site common street lamp LEDs work at
120V - 277V range.
If grid cannot provide stable 120V then LEDs has to wait 1 or more cycles until its capacitor charges enough for it to light. After it lights on its capacitor discharges and it has to wait again until it fully charges.
How to recreate such LED flashing at home?
No easy way i can think of. But there is youtube. You can watch some videos of people having dimmers installed at their own homes. While those would work with almost any conventional light bulb they had issues with cheap LED lights.
Epilepsy warning: You can see some examples when you write "dimmer", "led", "flashing", "blinking" into youtube search field i won't link examples because of epilepsy risk.
I had one such dimmer build before LED-s were common. Putting LED into socket and using dimmer at values other to 100% (or very close to 100%) would result in very heavy flicker, so i am sure that at least some people with dimmers do not fake their videos.
Conventional light bulbs are more more immune to voltage drops - those things would just dim a little bit.
How to recreate such conventional light bulb dim at home?
Take any device that requires a lot of energy such as electric kettle. At moment it starts.stops heating light bulb in same room should dim/brighten a little bit (sometimes it will take only few hz until it goes back). Use sunglasses or something to stare at light bulb the moment kettle turns on or off.