Sorry, something has gone wrong. try later whenever you're ready

I've a speaker-pair and have swithched the wifi on/off, reboot, did everyting en stil I receive the announcement: Sorry, something has gone wrong. try later whenever you're ready (in dutch) by the Google assistant. Can somebody tell me what's the matter and what I've to do?
Thanks very much. It's driving me crazy... :-|

Extra:
after 4 days of the above annoucement, today the question 'Hi Google, speel Radio 10' (dutch), worked. Then when I tried the same the next day, Google answered with 'Sorry, something has gone wrong. try later whenever you're ready' (in dutch).