@keneda Thank you! Strangely, I tried it again and it worked. The only thing I did differently this time was to create a small contacts.db (mine is 1.8 MB so I thought that the size might be the problem), move it into the directory and after a restart the contacts were shown. Then I deleted it, moved my 1.8 MB contacts.db into the directory and it worked. I have no idea why. I don't think my antics with the smaller file had anything to do with it. Anyway, thank you: Without your insistence that the contacts are saved in contacts.db I would not have tried it again.
Okay, I filed two bugs on Axolotl's GitHub. It's the first time I used GitHub so please forgive any mistakes, or point them out so that I can learn.
I hope it's helpful in any way. It's a worthy project and I'm eager to help it move forward. Unfortunately I can only help in small ways such as this.
I have tried the 'sledge-hammer' approach: delete all email accounts, uninstall Dekko2, clear residual Dekko files in .cache and in .config, reboot, reinstall, re-set up one IMAP account, and ...... same situation! [This is all on a brand-new (one week ago) installation of UT on a Nexus 5.]
PS Whilst rummaging through the file store I spotted folders relating to Evolution. Is this just some random hangover from Canonical's original ambitions, or is some version of Evolution available on UT?