What I tried in the mean time:
did a fresh install of nodebb on my test system withgit clone firstname.lastname@example.org:NodeBB/NodeBB.git -b v1.6.x
run through the setup procedure , but kept the redis database.
The problem remained.
Then Istopped nodebb stopped redis deleted the redis database files started redis run nodebb setup
That way I got a clean install without data and with default settings.
The problem still exists:
When you define a new reward the forms and pull downs are populated.
After saving the rewards, leaving the page and coming back, the pull down menus for existing rewards are not populated and empty, while creating a new reward works well.
After saving and reloading the rewards page, the error 'illegal reward. no inuts found' is displayed.
Last but not least, no rewards are awarded to users.