my minecraft server does not work, even though it is port forwarded correctly and runs properly

Question

I have a Minecraft server that I and a few of my friends play on. I have port forwarded correctly and the server will boot just fine. I am using NoIP's Dynamic User Client (DUC) to make my server joinable from a hostname (i.e. abcde.ddns.net). My server was working just fine with these settings, up until recently, my router reset. I was able to get it running and get into the server, but none of my friends were. I asked a friend who was not a member of the server to try and sign in and he was able to get in just fine. I have tried what seems like everything imaginable, from adjusting firewall settings to allow all java processes, to simple things like shutting off my computer, and for the life of me i cannot figure out why none of my friends can join. Here is information that may help in solving this:

#Fri Apr 03 13:28:10 EDT 2020
spawn-protection=0
max-tick-time=60000
query.port=25565
generator-settings=
force-gamemode=false
allow-nether=true
enforce-whitelist=false
gamemode=survival
broadcast-console-to-ops=true
enable-query=false
player-idle-timeout=0
difficulty=easy
spawn-monsters=true
broadcast-rcon-to-ops=true
op-permission-level=4
pvp=true
snooper-enabled=true
level-type=default
hardcore=false
enable-command-block=false
max-players=20
network-compression-threshold=256
resource-pack-sha1=
max-world-size=29999984
function-permission-level=2
rcon.port=25575
server-port=25565
server-ip=
spawn-npcs=true
allow-flight=false
level-name=world
view-distance=10
resource-pack=
spawn-animals=true
white-list=false
rcon.password=
generate-structures=true
max-build-height=256
online-mode=true
level-seed=
use-native-transport=true
prevent-proxy-connections=false
enable-rcon=false
motd=A Minecraft Server```

Answer 1

I like to attack these problems starting at the server itself and going outward toward the remote clients. Start with the absolute minimum to function and then add a piece at a time as you step toward a client that cannot connect. Every step proves that one part works or targets the part that is failing.

1. (Server test) Does the server startup properly? Does it have any error messages on it that indicate a problem? Most servers talk to Mojang to validate user UUIDs. This can cause issues on login when it is unable to talk to the internet.
2. (Local connectivity test) Can a machine on the same network login via IP address? This proves that the server can properly login. This will also prove that the server is still on the internal address that you are expecting (192.168.1.8 in your case). It is possible that its internal IP address might have changed (is your router that reset also providing your DHCP? Maybe it lost its table..) If this doesn't work, there could also be a local firewall blocking issue.
3. (Router test) Can a client outside your router (or your client if you can connect it to your phone or something) connect via IP? This test adds the requirement that routing, port forwarding, and the firewalling on your router are working properly. If your router is controlled by your ISP, they may have updated the firmware requiring additional setting changes.
4. (DUC test) - I am not familiar with this client in particular, but I am very familiar with DNS in general. To prove that it is working correctly, the machine must be able to resolve the DNS name to an IP. If you open a command prompt and ping it, it should show you an IP address on the outside of your router. This requests to Windows to get the IP for the DNS name the same way that Minecraft will. Note that you may get request timed out from ping. Many firewalls block ping and that is normal. This test is all about if ping can resolve the IP, not if it can actually ping.
5. (More distant remote testing) For the users that can't connect: Can they connect to another server? It's possible that the issues can have nothing to do with your setup.
6. If all of these tests pass, then you could have an issue with ISP blocking. There is nothing you can do but call them. With a bit of persuasion, you can get the front line people to forward a message to the engineers that can actually look at the problem. Honestly though, you are likely to get nowhere if this is your issue. Internet usage is way up at the moment, and so is their call volume.

Good luck