I think I have resolved the problem.
In the Settings menu in WHA, I went to the Network Status tab. I activated 'Preferred DNS server (8.8.8.8)
Currently, no stuttering and no failed tracks.
I remain unsure as to why everything worked fine before the latest WHA update, but as long as it works now I'm delighted.
Posts on What Hifi forum regarding Qobuz problems suggested resetting the default DNS settings in the router where this was possible. It appears Wiim were one step ahead