Issues with Workflow Manager CU4 installation

Workflow Manager CU installation- issues and fixes

I had to install the Workflow Manager CU on my Workflow Manager Farm. So I've checked the MS updates and found out CU5 was available to install. Support document
https://support.microsoft.com/en-gb/help/4055730/description-of-the-cumulative-update-5-for-workflow-manager-1-0.
So I've checked the support document and it says:
"Workflow Manager Client 1.0 CU4 is a prerequisite for Workflow Manager 1.0 CU5. It can be downloaded from Cumulative update 4 for workflow manager 1.0 (KB4019220)."

So, I followed the instruction and installed the CU4 and never checked the instructions on CU4 (CU4 says it has a prerequisite of CU3 and so on). CU4 installed successfully didn't warned me about missing CU3. And after CU4 installation 😞 Workflow Manager Backend service started throwing error while starting and never started again. Event Log displayed error in every 30 seconds.

Application: Microsoft.Workflow.ServiceHost.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.IO.InvalidDataException
   at Microsoft.Workflow.Common.AsyncResult.End[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]](System.IAsyncResult)
   at Microsoft.Workflow.Service.WorkflowServiceBackendHost.OnStartCompleted(System.IAsyncResult)
Exception Info: Microsoft.Workflow.Common.FatalException
   at Microsoft.Workflow.Common.Fx+<>c__DisplayClass2.<FailFast>b__0()
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
   at System.Threading.ThreadHelper.ThreadStart()

AND

Faulting application name: Microsoft.Workflow.ServiceHost.exe, version: 1.0.20922.0, time stamp: 0x505e1b24
Faulting module name: KERNELBASE.dll, version: 6.3.9600.19425, time stamp: 0x5d26b6e9
Exception code: 0xe0434352
Fault offset: 0x000000000000908c
Faulting process id: 0x34d8
Faulting application start time: 0x01d5535082cb5ad7
Faulting application path: C:\Program Files\Workflow Manager\1.0\Workflow\Artifacts\Microsoft.Workflow.ServiceHost.exe
Faulting module path: C:\Windows\system32\KERNELBASE.dll
Report Id: c0bd0ad8-bf43-11e9-81b6-000c29d638a9
Faulting package full name: 

Faulting package-relative application ID: 

So, I've checked the CU5 support document, there is a section Issues that are fixed in this update, it says:

Workflow Manager 1.0 CU4 cannot be directly installed from versions that are earlier than Workflow Manager 1.0 CU3. This update fixes the issue and makes sure that Workflow Manager 1.0 CU5 can be installed on top of any earlier versions.

Quite confusing 😕, as in the Notes section it says CU4 is a prerequisite and here it says it's going to fix the same issue. So I thought of giving a chance to CU5 to fix the issue created by CU4 and installed the CU5. Voila 😊 it fixed the issue and Workflow Manager Backend Service again started working.

So, now I think CU5 doesn't need CU4 to be installed on Server, you can directly install CU5 and it will work.