When you restart Explorer (say, by using using Task Manager) then you lose any opened folders you have.
I had begun using Winaero‘s tiny (8KB) RestartExplorer which does the same but is quicker.
However, as I often have a lot of open folders I now use Sordum.org‘s Restart Explorer. This is because it saves any open folders before restarting Explorer then re-opens the folders again after Explorer restarts. IMO this is even more convenient and saves me having to remember what folders I had open.
Hope this helps… .