Calibre content server eReader not saving highlights

Hi All - I recently stood up a new Ubuntu server instance of calibre-server to serve up my collection of 1,000 books over the web. Everything is working perfect except for one thing -- The web based reader will not save highlights!

I can highlight text, but when I close the book and reopen it, the highlights are gone.

Here is the contents of my calibre-server conf file -- any input is appreciated!

-----------------------------------------

## startup service
[Unit]
Description=calibre content server
After=network.target

[Service]
Type=simple
User=dave
Group=dave
ExecStart=/usr/bin/calibre-server /mnt/external/Dropbox/Libraries/Books --enable-local-write --enable-auth

[Install]
WantedBy=multi-user.target