Cannot access thru hairpin NAT from LAN to a particular IP [closed]

Question

An enigmatic issue drives me nuts.

I have a setup like this:

Internet <-> ISP router 192.168.1.1 <-> 192.168.1.144 Unifi USG-3P 10.27.0.1 <-> 10.27.0.50 Reverse proxy 10.27.0.50 <-> 10.27.0.40,10.27.0.50 HASS servers.

Everything was working fine until yesterday.

Now I have no problem connecting to those HASS servers from internet. But I cannot connect to them from within the LAN.

Strangely, I have found that it affects only the IP address of the reverse proxy. I added a few port forwarding on both the ISP router and USG-3P for testing. All worked well while the connections were made from internet. OTOH, when connecting from LAN thru hairpin NAT, all connections worked except those connecting to the IP address of the reverse proxy.

The USG-3P logged those failed connections and the destination IPs were listed correctly. Unfortunately, the access logs of the reverse proxy and other processes on the same IP did not record any traffic.

Could someone please give me an insight on how to resolve this puzzle?

Many thanks!