Maybe a little late to reply but just upgraded to 18.04 and also owner of a Perfection 300 which deliver good service for a longtime. The problem is linked to a missing udev rule. Sane project nor iscan ( Avasys) have this scanner model in their database. By issuing 'lsusb | grep -i epson' command I was able to add the following rule file in '/etc/udev/hwdb.d'
$ cat /etc/udev/hwdb.d/21-epson300photo.hwdb
# Epson Perfection 300 | Epson GT-F720 | Epson Perfection 300 Photo
usb:v04B8p0131*
libsane_matched=yes
$ ll /etc/udev/hwdb.d/
total 12
drwxr-xr-x 2 root root 4096 sep 17 00:01 ./
drwxr-xr-x 4 root root 4096 sep 17 00:18 ../
-rw-r--r-- 1 root root 106 sep 16 23:59 21-epson300photo.hwdb
$ sudo reboot
Now enjoy 