I keep getting kicked from a realm server due to java internal exception error

I am currently playing Minecraft Realms on 1.16.1 Java edition and the last week or so I have not been able to play due to this error message: Internal exception: java.io.ioexception an existing connection was forcibly closed by the remote host.

I connect and the game takes up to a minute to load in the world before it finally loads in my items. I am always kicked right after this. The realm is owned by my neighbour, and he as well as the other guys on the server are having no issue. We share the same ISP and our modems are all the same, a TP link modem.

So I started searching around and attempted the following fixes:

• Allowed all Java and Minecraft-related applications through my firewall.

• Updated Java as well as checked for updates for everything else and updated where necessary.

• Opened ports 26-28000, 80 and 443 (a common fix according to this article: https://help.minecraft.net/hc/en-us/articles/360035130871-Java-Edition-Realms-connection-issues-).

• Disabled my firewall completely to see if it fixed the issue.

• Enabled the native sandbox in java settings.

• Enabled NAT acceleration (a common fix according to a comment on here: https://www.reddit.com/r/Minecraft/comments/432m1f/fix_for_internal_exception_javaioioexception_an/).

• Contacted my ISP, who claimed that it could be an IP issue, so they bridged my antenna and modem to ensure that they always run on the same IP address.

And that`s about it. The only thing that works is using mobile data through a hotspot, but I`m all out of data. So it`s obviously something wrong with the internet connection. However, Minecraft realms is the only game where I`m having issues. Regular Minecraft multiplayer servers? No problem. Same goes for virtually every other game I play online (CS:GO, FIFA, Rust, etc.). So I`m kinda lost here. I don`t know what to do, and would really appreciate some help.