Comment 9 for bug 1672166

Hmm, everything appears to work as expected but when it's time to learn, there is no attempt being made. It's as if learning was turned off or paused, but looking at your settings, that clearly isn't the case.

I can't reproduce this on Zesty, will do some tests on Ubuntu 16.04.

It has to happen somewhere on the path from WordSuggestions.commit_changes() to WPEngine.learn_text(), but I can't tell where or why at the moment.

If you feel adventurous, add some print("hello 1") statements and find out where commit_changes() and below exits without learning.
$ sudo gedit /usr/lib/python3/dist-packages/Onboard/WordSuggestions.py /usr/lib/python3/dist-packages/Onboard/WPEngine.py

I'll add some more debug output anyway.