Unable to access FTP after upgrading computer

Until recently, I was using a Late 2013 iMac running the latest version Catalina as I was no longer able to update any further. Two weeks ago, I had a hardware issue with it and finally upgraded to the latest Mac mini M2 Pro and now running macOS 13.5. I am now having an odd issue where I have a lot of difficulty accessing an FTP server I had no issue at all accessing before on my older iMac. I would connect to the FTP server using CyberDuck or FileZilla Pro. Occasionally, I would experience an issue where the server was down for a while. But what I'm experiencing now is not that at all.

If I can't connect, I will get a message on Cyberduck saying, "Connection closed without indication. The connection attempt was rejected. The server may be down, or your network may not be properly configured." And FileZilla just keep trying to connect over and over. If I leave the server alone for a while, it eventually does let me connect. But once I start trying to download files from it, it constantly asks for my login over and over, and then my transfer eventually fails to complete. I disconnect from the server, try to connect again, and get the same message as above. Since upgrading to the new Mac mini, there have been instances where it would let me connect and download successfully, although extremely slow.

I reached out to the host who told me there is no issue on their end with my IP being able to access the server. But then eventually said my IP has been getting blocked again and again. I reach out to my ISP who told me there were no kind of blocks on my network. I am using the same Netgear modem and Google Wi-Fi on Ethernet and Wi-Fi I was using with my old iMac. I have completely restarted my modem and Google Wi-Fi. I started up Parallels running Windows 11 to essentially try a different computer, and tried using FileZilla on there. I connected to various VPN locations all over the world. I also changed the DNS on both my Ethernet and Wi-Fi network. Every one of these attempts still had the same result. I know this is specific to my network because I can connect to the server using an FTP app on my iPhone 12 Pro Max running the latest version of iOS, but only if I'm using the cellular network. If I'm connected to my Wi-Fi, it still fails.

At this point, I'm completely out of ideas. Nothing has changed about my setup except for changing out my old iMac for the new Mac mini, which I restored from a Time Machine backup from my iMac. I can't imagine there being anything about my Mac mini that could have caused this to occur. But that is the only difference since I've started to experience this issue. Can anyone offer any kind of suggestions?