Preferred "NAT Loopback" method?

[D34DC3N73R]

I have an RT-AC88U running asus merlin 386.3_2. For the longest time, NAT loopback seemed to be working just fine for me, but it stopped working for me today. I know the setting was removed from the firewall section in 2018, and I've tried to read any other threads in regards to NAT loopback. I've seen several suggestions but I'm unsure of which one is the preferred method. Ideally, I'd like to keep NAT acceleration on if possible. I'm not sure why nat loopback was working and just decided to stop today, but I'd like to get it back if possible.
Background: I have a home server and run several services as subdomain reverse proxies that I'd like to access on my local network rather than using IPort.

 

[ColinTaylor]

As this has been working for some time and has suddenly stopped without any changes to your router I think it's safe to say something has changed outside of the router. So the first thing to not do is change anything on the router.

So what has changed? The most obvious thing would be your external IP address. Are you using DDNS? Does DDNS resolve to your current WAN IP address? Any software updates to your PCs or servers?

 

[D34DC3N73R]

My WAN IP is the same as it has been for quite a while. I use a custom DDNS with Cloudflare and a script that updates the WAN IP on router boot. All domains/subdomains resolve fine out of network. I did some application and docker image updates on the server last night but it was running fine after.

So this is where it gets weird.

Realizing NAT loopback wasn't working, I decided to use pi-holes (I have 2 on my network) local DNS feature. I entered my main domain and a single subdomain. Tested both the URLs and each resolved fine. However, that meant I would have to enter each subdomain which I wasn't looking forward to. This is when I went down the rabbit hole here trying to figure out a way to get something in place of NAT Loopback (maybe using iptables etc). I wanted to check to see if there was maybe a non GUI setting that might be causing this, so I ran `nvram show | grep nat`. I saw `nat_redirect_enable=0` and wasn't sure what that was, so I started researching it, this is when I noticed a notification come in from a service that relies on being able to resolve my domain on the network. Sure enough, I tested more of my subdomains and they all appear to be working again. I have no idea what caused them to stop working and no idea why they started working again...