My RTMP Server on Stream PC works remotely with GoPro Quik App for streaming but not on other streaming apps (Moblin, Streamlabs)

Hello everyone! I've done lots of testing on this for the past few days but still can't understand why this isn't working. So I figured I'd post it here in hope that someone has encountered the same or something similar before and has a solution.

*FULL STORY*

I'm trying to do some IRL streaming from my iPhone 12 Pro Max. Its updated to the latest iOS (17.4.1 at the time of this post). I've set up everything on my Stream PC at home correctly with nginx server, OBS, and port forwarding on my router. When I tested the GoPro Quik App at home with the GoPro 10 Hero, I entered the RTMP url (rtmp://MY_LOCAL_IP:1935/publish/live) and it works, video and audio are showing up just fine on OBS on the Stream PC. Then I tested it again remotely (not connected to Wi-Fi). I entered the RTMP url (rtmp://MY_PUBLIC_IP:1935/publish/live) and again, it works. So this tells me that port forwarding and nginx on Stream PC is set up just fine and its working on both local network and remote network.

Due to the unreliability of streaming with the GoPro through the GoPro Quik App (whenever the stream is interrupted, the stream disconnects and then you have to go through the whole process of connecting the GoPro back to the phone and start the stream again), I've decided to try using an IRL streaming app. I downloaded Moblin first. I did the same testing that I did with the GoPro: tested on local network (rtmp://MY_LOCAL_IP:1935/publish/live) and it works just fine. However, when I disconnected from Wi-Fi, and entered the remote RTMP url (rtmp://MY_PUBLIC_IP:1935/publish/live), it does NOT work. It keeps saying that it fails to connect. At first, I thought I didn't type it in correctly. But after checking the url, re-typing it multiple times, and even copying the url from the GoPro Quik App that works, it still says failed to connect. I even reconnected back to Wi-Fi and tried the Local IP url, and it still works. Its just the Public IP url not working, even though it works just fine on the GoPro Quik App.

Then I tried StreamLabs app, and it does the exact same thing as I've described above: Local IP RTMP url works just fine but the Public IP RTMP url does not work even though it does work on the GoPro Quik App.

The only information I have to explain the difference of why the GoPro Quik App works fine remotely but the others do not is because through the GoPro Quik App, the GoPro itself is connected to my iPhone's hotspot. Yet, the apps are not, just goes through regular Cellular Data. Based on this information, its obvious that my Internet Service Provider (ISP) at home is not blocking anything because if it was, the GoPro wouldn't work remotely. Also, I've already checked the permissions on the Moblin and StreamLabs, and they both have access to cellular data just like the GoPro Quik app does.

Based on all this information, I'm thinking its being blocked either my iPhone itself or my cellular service provider. Before going through the process of contacting my cell service provider, I wanted to see if anybody has encountered something like this and has any ideas to try.

Thank you so much in advance!