Cloudflare send permanently TCP RST only on my new ISP over FTTH

Hello,

I have been using Cloudflare for a few years. So far I was also very satisfied. But with the change to FTTH and a new ISP, I can no longer establish a stable connection to Cloudflare. Both my servers, and others, such as “Escape from Tarkov”, I can no longer connect stably.

Every 1 to 10 seconds Cloudflare sends back a RST. The client then reconnects. Which causes a new port to be used. Cloudflare then tries parallel to send a TCP retransmission several times on the old port. This is then eventually rejected by my FritzBox 5590 with “Destination unreachable”.

At first I had DS Lite with a local IPv4 address. What I have criticized and I could then book a fixed IPv4 address for more money. But that did not bring anything.

If I use a VPN over FTTH, or other internet connections like DSL, cable or GSM, I can then access Cloudflare without any problems.

I have reported the problem to my ISP. As already described, attempts were also made to fix this (Fixed IPv4 address). I also sent packet captures to my ISP. But now I have not received any answer for 10 days. It is maybe not the ISP fault, but Cloudflare? Can it be that the IP address of my new ISP at Cloudflare are marked as bad, or something else? Or do I have to make more pressure on my ISP, because he is to blame?

For example, my ISP uses this IP address space 185.55.73.0 - 185.55.73.255

Here is an example of a package capture:

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