hope you are well :-)
The error is hard to troubleshoot with only the message you posted. Basically this indicates that MWG has not received a valid HTTP response when trying to talk to the server. There are basically two possible reasons for this, which are both hard to troubleshoot:
1.) MWG does not retrieve a valid HTTP response. This means the request is not correctly transferred to the remote server or the response is broken. It could be broken on the server (server sends invalid data) or gets broken in transition (some network device breaks the response)
2.) MWG retrieves a correct HTTP response, but an error in the product causes MWG not to show the page correctly.
It would be helpful if the problem can be reproduced in a test environment with only few users. To see the response MWG receives from the Internet a packet capture would be helpful. In this case support will probably be your best point of contact, since they can review the response MWG received :-)
thanks for the answer, and - yes, we opened now a ticket for the support.
Since friday the problem increases, now I got several URL´s, with which the problem can be reproduced. I fear a bigger problem as it seems right now - not only for Wuppertal. I hope, some tcpdumps and feedback-files are helpful for the support.
Again thank you for your fast answer and have a nice week.
Greetings from Wuppertal
as far as I heard Alex helped to find out that there seems to be a bug in MWG in regards to IPv4/iPv6. I hope the issue gets resolved soon :-)