Thanks to all for your thoughts, especially the canalplanac forum link. After talking to Microsoft support It's beginning to look like there is a problem on the PC (Microsoft Surface Pro 6) that is affecting this, though the PC fault is intermittent and random but canal plan ac is reacting completely consistently in failing to give me route plans. By the way I am registered with canal plan ac and automatically log in when using it on the PC as I mostly travel single-handed so I have my own settings for hours per day, lock times, etc.
Once again, thanks for helping me isolate the problem.