Issues with sendfile()?

Since a few months ago I started experiencing an annoying issue with the Telegram Desktop application. In short, the application updater downloads the binary for the new version, but then fails to copy the file from the temporary directory into the installation directory. Only some part of the file is copied.

The issue is discussed in details at GitHub of the application, and the application developers insist that what is failing is the sendfile() system call.

I am currently on Fedora 34. I update my system frequently, and had this issue with a number of different kernels. What is also worth mentioning is that I have another machine with Fedora 34, and there this issue never happened.

What can I do to diagnose the issue or to help the kernel maintainers to diagnose it?

I guess the first test you could do is, to create a new user on the machine with the problem and see if it happens there too.