Hello,
If you use a Windows Server, check that the mime types are maintained and that there are no problems. Check the web server log, if it is receiving the requests correctly, the problem should appear there.
1) I have downloaded the source code and we have moved it to Net Framework 4.8.1 to make it compatible with the new communication protocols, apart from some editions adapted to what we need.
2) What is happening to you is very strange, I will need some more information to know what is happening, but you should check the log or even if you have cloudflare or some firewall to make sure that it is not blocking the request.
In the same error in the update window, it should tell you what error is returned, if it is 404 or what type of error.
Share some more information so that we can find the problem.
If you are using the automatic updater, it has many problems and will be discontinued in the next version that is being worked on.
Run WyUpdate.exe directly when the program generates it, but if you use more modern protocols, download the source code here,
https://github.com/wyday/wyupdate
Compile with the new 4.8.1 framework. The executable you generate must be used where you are deploying your updater.
As I said in the previous message, I need more information, but we will go step by step to find out what is happening, if it worked before and now it doesn't.