There is a nice tool for updating your db (mine is MySQL) with a tool called texturecache

this info is for my own purpose if useful use it

Crontab in place

0 */2 * * * sh /home/kodi/kodiupdate.sh > /dev/null 2>&1

#!/bin/bashNAME=texturecache
INIT_DIR=/etc/init.d
echo “Start Scanning Video Library vscan”
/home/kodi/texturecache.py vscan
sleep 5
echo “Start Cleaning Video Library vclean”
/home/kodi/texturecache.py vclean
sleep 5
echo “Start update with qax”
/home/kodi/texturecache.py qax
echo “Start scanning texturecache with function C”
/home/kodi/texturecache.py c
sleep 5
echo “Prune data missing on disk P”
/home/kodi/texturecache.py P
sleep 5
echo “Start update with Xd”
/home/kodi/texturecache.py Xd
sleep 3
echo “Start update with ./texturecache.py R”
/home/dennis/kodi/texturecache.py R
sleep 3
echo “end”

Make sure that there is a connection with your “Master Kodi”
create a samba link in /etc/fstab ie. example
//192.168.1.115/Userdata/ /media/kodi cifs guest,uid=1000,iocharset=utf8 0 0
now the thumbnails can be saved correctly