Browsers sometimes opening on wrong monitor

Not a show stopper, just annoying. Two of my browsers, Vivaldi (Chrome based) which I use most of the time and Chrome both open on my no. 3 monitor. Doesn't happen all the time... maybe one out of every ten times I open them and occasionally when I minimize then maximize them during use. Always on the no. 3 monitor, never no. 2.

I always close them on my no 1/main monitor but that makes no difference. I usually have my no. 3 monitor off because I don't use it often so that's the main reason it's a bit of a pain.. I have to turn it on to grab the browser to drag it back to my main monitor. If I had the monitor on all the time I wouldn't really care that much.

Shift/right clicking on the taskbar icon to move the browser doesn't work because "move" is always grayed out.

It happens randomly, sometimes just after I boot and sometimes after the PC has been running the whole day.

Monitors 1 and 2 are controlled by my main GPU and no. 3 is on it's own GPU (both MSI) . It's been happening for a few months and didn't appear to be caused by any Windows OS updates (I only install the important security related ones anyway). All the graphics drivers are up to date.

I have no third party software that controls my desktop environment. It's all standard Windows settings.

So to summarize only happens with my two Chrome based browsers, never FireFox or any other program for that matter and always monitor 3.

tnks.