sfdx force:source:pull Entity of type 'CustomApplication' named 'Case' cannot be found

This is a bug I feel somewhere in the sfdx cli and one needs to bring it attention to Salesforce on this.

The following is a workaround that did actually work for me .

• I created an application named 'case' in my scratch org

• Run `sfdx force:source:pull.

• Add the folder path of the application in .gitignore and in .forceignore files.

Note that with this workaround I was able to get past this issue.However it is definitely a bug in salesforce CLI which I request you raise a support case.

Update

Any thing you want to exclude when you run force:source:pull you can do so by deleting the Member from Source Member object.

Use Developer console to execute below query

Select Id, MemberName From SourceMember Where MemberType = 'CustomApplication

and Delete it in the Dev console.

Just happen to me too. Seems like its a known Issue - Only way I managed to remove this error was remove/delete the SourceMember.

sfdx force:data:soql:query -q "Select Id, MemberName From SourceMember Where MemberType = 'CustomApplication'" -t

Then Delete with the result Id.
sfdx force:data:record:delete -s SourceMember -i 0MZ1** -t -u orgAlias

An alternate (as the OP was attempting) would be to add to the .forceignore file. I believe this is the entry that's needed (though the syntax is confusing and case-sensitive... with next-to-zero docs)

Case.CustomApplication