I have had sporadic problems with Vodafone Germany’s IPv4 routing for months, sent detailed analyses and refused in advance to pay for any technicians they might send because the problem could not be on my property. They sent two technicians who confirmed my view. Then they charged me 160 EUR for them without fixing the issue.

You have to go to forum.vodafone.de:

1. State stat the error also occurs with the Vodafone router.

2. that you already have done a factory reset of the Vodafone router.

3. that you already have turned your Vodafone router off for 24 hours and it didn't fix the error.

4. that you already talked to the hotline multiple times.

After that you have to pray that someone with the same problem comes along and endorse your problem. Like, "I have the same problem since...". This sometimes conjures a Vodafone guy who tells you he has informed the technicians. Than you have won and within less than a day the error is gone.

I was six month without IPv6 even though the error message was clear. The forum route finally worked.

They are NATing the IPv4s, i.e. multiple customers are sharing the same IPv4, which can cause problems. I called them and told them that I absolutely need to do port forwarding and asked nicely if I could get an exclusive IPv4. The support said „Of course, let me check the box in the UI for your account, should be active by tomorrow“ and done. You have to get lucky to get someone who understands your problem and is willing to fix it, though.