Are there any updates on this? I tried filing a code level support incident on the same problem last November, but Apple closed it without even bothering to respond to me.

I am wondering how exactly that Ruby gem affects the Xcode build system that gets invoked as source files are being changed. In particular whether it hooks into the standard Xcode services or build scripts in some way.

So, sudo gem update xcodeproj is not helping in your case?

This seems to be fixing the problem for me as well... (fingers crossed).

Although it became somewhat better in 14.1 RC, it's not fixed completely - I have errors and warnings still disappearing in some cases.

That's quite weird... Because the I am having this problem on an Intel machine. Maybe, there is some sort of race condition going on, and lowering performance alters the timing, etc.