Thanks to chewitt - in another thread he explained how to use a own samba.conf
I did:
edit samba.conf.sample ( /storage/Configfiles )
added
[Storage]
path = /var/media/STORAGE
available = yes
browseable = yes
public = yes
writeable = yes
renamed (copied) samba.conf.sample -> samba.conf
reboot
it works again. Thread solved 
P.S.: Updated to 10.0.2 meanwhile.
P.P.S.: Funny thing, after rebooting two times with new samba.conf auto-share external drives worked again
Same for me 
LE 10.0.1 -> no update to 10.0.2
Same for me...
RPi 4, Libreelec 10.0.1, boot from SD card, USB 3 SSD (still LE 9.2 on it)
It worked for a few days, had access via SMB to /STORAGE and /LIBREELEC on SSD (auto-share enabled).
Both folders are gone since last week, all folders of SD card are there, SSD mounted, tested with Mac OS Catalina and Win10.
Still have access to another machine with a RPi3 and LE 9.2, an auto-shared USB Stick is visible.
Please help
