When I restart my iMac with OS High Sierra some windows are not where they are supposed to be...

Hi all,

i have an iMac 2017 with OS High Sierra, with a 2nd display.

Normally on the second display I have Mail, Safari... now, when I turn the iMac on, all the app i normally run on the second display appears in the iMac monitor instead... (with OS Sierra not) and this cause me each time a loss of time moving the apps in the correct place...

Does it exist a solution?

thx a lot

cheers

g