Build service could not start build operation: internal error: failed to send the system info to the build service

I think your Xcode is just in the process of indexing the files. It may take some time to finish but when it's done, just give it a try.

If it's not helpful, try reopening your xcode - it works for me after the indexing process finished.

No needs to restart system. Just restart Xcode -> clean build fix this issue for me.

Restarting my Mac was the only solution for me. Restarting Xcode did not fix. We are back to Microsoft days.

Very very strange, you may laugh while reading my answer but restarting my laptop did the trick for me, I was trying to make ios build in my ionic1 app

In my case opening 2 projects at a time using Xcode got the hitch. So I closed all and opened one then it was working fine.

I commented above but thereafter figured out another possible solution to try. Cleaning the project worked. (I restarted XCode10, my computer, and waited for indexing to finish - neither of these worked for me, at least.)

Command + Shift + K

or equivalently

Product > Clean Build Folder

I quit my Xcode and delete some file related to Xcode and empty the bin. Then I open a Xcode project. Its working fine for me.

Go to File --> Workspace Setting --> Change "Build System" to "Legacy Build System" from "New Build System