WPAD connection is delayed

I use my laptop on WIFI (blue network) and on LAN (green network). For the green network the web proxy is active (non transparent).
If I connect to the Internet via WIFI and firefox the responsiveness of the internet is perfect, but if I connect via the green network and use WPAD (via DHCP) the responsiveness is distinctly delayed. Which is not the case if I define the proxy in the firefox manually.
What is the reason?

ipfire 160
opensuse 15.3
firefox 78.13 esr