Browser Start Up

I’ve 7 tabs pinned in the tabs section of the browser for sites I regularly visit. Every few days when I open the browser, I notice all my pinned tabs have disappeared and I have to repin them again.

I’ve just had a power outage, which lasted less that a second, when I rebooted the PC I went straight to my browser only to find all my tabbed pins had gone.

Can someone offer an explanation?