Captive Portal makes HA Proxy unfunctional

[dnut]

Hello,
I'm experimenting with Captive Portal, and I'm noticing HA Proxy stops working as expected if I activate Captive Portal.

I'm using HA Proxy both as HTTP and HTTPS reverse proxy.
HA Proxy works as expected, but the HTTP side stops working if I activate Captive Portal.
HTTPS side of HA Proxy continues to work as expected.

HA Proxy frontend is on WAN1
HA Proxy backends are on LAN
Captive portal is set up on LAN2

Any idea?

Thank you