S8 Lock screen too bright, any idea why?

[Silverstonez]

I have a Samsung s8 and recently a new problem has arrived.

At night I turn the brightness right down for driving but whenever the phone locks and I turn it on, the screen is very bright for a few seconds. Once it enters normal operation the brightness dims again automatically after 2 or 3 seconds but by then I've been blinded.

I don't recall this ever being a problem before, previously if I lowered brightness then my settings were universal across the phone.

Have I changed a setting, is it a bug? Is there a fix?

Thanks