File Explorer folder windows not always restoring on switch on

Hi

Increasingly of late when I fire up my Inspiron 5767 I find the File Explorer folder windows I had open when I switched off aren't back where they were. 

It's not every time.

I usually keep the same 6 or 7 folder windows open for folders I often use. Really annoying to find them all gone.

Thought it was just on Sleep when I triggered that by closing the lid but tried triggering via Start Menu and had the same issue. Then also happened after full shut-down and later re-start.

I have "Restore previous folder windows at logon" ticked.

Any ideas folks?