File explorer hangs after lost of network connection, NAS related prblem

I have mounted NFS share on my computer. When I lost connection (e.g. turn off wifi, disconnect cable, no route) then opening file explorer takes at least 10 minutes(sic!), listing directory with ls /nas also is blocked. I was trying with many options in /etc/fstab, e.g. fg, retry, async, timeo, retrans, but it doesn’t help.

Current fstab entry:

10.70.1.1:/mnt/vol0/data /nas nfs rw,fsc,vers=3,bg,user,retry=0       0       0