Issue Fixed: Files Server not connecting to PC shared Folder

This solved my issue:

• On your windows machine, go to Network & internet>Status>Properties (of your current home wifi) and scroll down to 'random hardware addresses' and make sure 'use random addresses for this network' ticked to 'off'. I'm not sure if it's on or off by default, but mine was set to 'daily'. In theory of course it's good to keep this on, but it will change your IP address each day (hence why you could at one point access the server, but no longer can), and therefore will disconnect your Files from the shared folder you're wanting to access.
• After you turn that off, you'll need to get your current IPv4 again. You can do this any way you know how, but the most convenient way is to just scroll down in that properties page you're already on, and your IP4v address should be right there.
• Also, I think toggling that IP thing boots off your shared access to your shared folder. I had to go back into my shared folder (on windows PC still) and re-add my shared user the way I did originally.
• Finally, go back to your iPhone Files app and add a 'new server' and type in your new IPv4 address, log in as your registered user, and it should connect.

Hope that helps like it did for me.