Hi all,
I can launch a disable workflow,
I don’t know what to do.
Welcome to the community @Christel_Doudet !
I have never seen anything like that before. Can you please provide some additional information about how, and with what settings you run n8n exactly? Also if it is possible that you maybe have two n8n instances running at the same time.
Find it !
A proxyserver was not correctly configured and accept cache data on get request. 
Great to hear that you found the problem. Also thanks for posting the solution. Will be helpful for other people with a similar problem.
Have fun!