Wireguard Client over IPV6 endpoint

Installing and Using OpenWrt Network and Wireless Configuration
11

Router A (only provides a connection to the internet, nothing more)
192.168.178.0/24

Router B (is connected to router A via wan 192.168.178.22)
192.168.1.0/24
The Wireguard server runs on router B (100.64.0.1)

Router C
192.168.8.0/24
router C should be used as a mobile device and connect to router B via wireguard and should reach all devices from the 192.168.1.0/24 network

For testing I connected router C to router A and specified 192.168.178.22:1234 as the endpoint. Everything works perfectly.

However, if I take router B's public IPV6 as the endpoint, I can no longer access WebUi and other services.

ping from router C to router B -> works
ping from router B to router C -> works
ssh from router C to router B -> works
Webui from router B via router C -> not working
That is what I don't understand.....

Wireguard Server:

interface: wg0
  public key: ************
  private key: (hidden)
  listening port: 1234

peer: *******************
  endpoint: [2a03:****:**:***:****:****:****:****]:39252
  allowed ips: 100.64.0.3/32, 192.168.8.0/24
  latest handshake: 1 minute, 57 seconds ago
  transfer: 199.91 KiB received, 407.26 KiB sent

peer: ***************
  allowed ips: 100.64.0.2/32

peer: *****************
  allowed ips: 100.64.0.4/32

Router C Wireguard Client:

interface: ASUS_MANGO
  public key: **********
  private key: (hidden)
  listening port: 37716

peer: ****************************
  endpoint: *************:1234
  allowed ips: 192.168.1.0/24, 100.64.0.0/24
  latest handshake: 1 minute, 59 seconds ago
  transfer: 748.03 KiB received, 520.75 KiB sent

Edit:
This problem does not seem to have been there for the first time:

However, the solution has not been said, or there is none.