Q:

The "ConvertResourcesCases" task failed unexpectedly. Xamarin Android build

When I build my Xamarin Android app with Visual Studio 2017 for Mac(7.7.4 build 1), Mono JIT compiler version 5.18.0.248 (2018-08/a4956c837e1 Fri Jan 25 16:13:12 EST 2019) I get the following exceptions:
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018: The "ConvertResourcesCases" task failed unexpectedly.
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018: System.IO.IOException: Could not create file "/Users/username/Companymobil/src/Company.Recipes.Droid/obj/Debug/lp/35/jl/res/values-ca/values-ca.xml" or "/var/folders/b5/821mhz8n0px17rnxglrjq5mc0000gp/T/tmp565e9644.tmp". File already exists.
/var/folders/b5/821mhz8n0px17rnxglrjq5mc0000gp/T/
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at System.IO.File.Copy (System.String sourceFileName, System.String destFileName, System.Boolean overwrite) [0x00193] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/mono-x64/mcs/class/corlib/System.IO/File.cs:111 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.FixupResources (Microsoft.Build.Framework.ITaskItem item, System.Collections.Generic.Dictionary`2[TKey,TValue] acwMap) [0x00204] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.FixupResources (System.Collections.Generic.Dictionary`2[TKey,TValue] acwMap) [0x0000f] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.Execute () [0x000a7] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00023] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/msbuild-15/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs:573 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x001f6] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/msbuild-15/src/Build/BackEnd/Components/RequestBuilder/TaskBuilder.cs:784 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018: The "ConvertResourcesCases" task failed unexpectedly.
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018: System.IO.IOException: Could not create file "/Users/username/Companymobil/src/Company.ServerAnnouncement.Droid/obj/Debug/lp/15/jl/res/layout/notification_template_icon_group.xml" or "/var/folders/b5/821mhz8n0px17rnxglrjq5mc0000gp/T/tmp4d4475a7.tmp". File already exists.
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at System.IO.File.Copy (System.String sourceFileName, System.String destFileName, System.Boolean overwrite) [0x00193] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/mono-x64/mcs/class/corlib/System.IO/File.cs:111 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.FixupResources (Microsoft.Build.Framework.ITaskItem item, System.Collections.Generic.Dictionary`2[TKey,TValue] acwMap) [0x00204] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.FixupResources (System.Collections.Generic.Dictionary`2[TKey,TValue] acwMap) [0x0000f] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Xamarin.Android.Tasks.ConvertResourcesCases.Execute () [0x000a7] in <78f051a6e2064f849cc3ee585300af39>:0 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00023] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/msbuild-15/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs:573 
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1689,2): error MSB4018:   at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x001f6] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-08/external/bockbuild/builds/msbuild-15/src/Build/BackEnd/Components/RequestBuilder/TaskBuilder.cs:784 

If I click on Build (NOT Rebuild) those exceptions get less every time I build until it finally builds successfully.
If I use jetbrains Rider, the build works every single time. 
I gave full permissions (r/w) to everyone on the directories mentioned in the exception and I still get the error. I use APFS case-insensitive.
I would be very grateful for any pointer to solve this.

A:

Thank you very much Leon Lu from Microsoft for pointing me in the right direction. The error stems from a condition in parallel building xamarin android. When parallel builds are disabled, the outcome is the same each time. Parallel builds can be disabled in the Preferences of Visual Studio 2017 for Mac (see attached image).
The issue seems to be fixed (see GitHub link in Leon Lu's comment) and be rolling out in one of the future updates.

