Build crashes when running multiple msbuilds in parallel

I am running a script to build a big project with msbuild (using qt).

When I try to build another project that uses Qt at the same time (from devenv) I get these errors, which prevent the build from succeeding:

3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: The "CriticalSection" task failed unexpectedly.
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: System.UnauthorizedAccessException: Access to the path is denied.
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at System.Threading.EventWaitHandle.OpenExistingWorker(String name, EventWaitHandleRights rights, EventWaitHandle& result)
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at System.Threading.EventWaitHandle.TryOpenExisting(String name, EventWaitHandle& result)
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at InlineCode.CriticalSection.Execute() in c:\Users\job\AppData\Local\Temp\it4lx0db.0.cs:line 67
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
3>C:\Users\job\AppData\Local\QtMsBuild\qt_globals.targets(575,5): error MSB4018: at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()

I quite frequently build multiple things at the same time, so this is pretty annoying.

I also don't understand why these 2 completely different processes have any kind of interaction at all. Any temporary files they use should be unique, not shared.