On RHPAM 7.12.1 a process with Document marshalling strategy using org.jbpm.document.DocumentCollection creates variables of type org.jbpm.document.Document named "varname (pos/count)" for each uploaded document.
On Business Central UI (Process Instances > {select the instance} > Process Variables) for each "varname (pos/count)" there is the History button: [^history_btn.png]
When this button is clicked, a Dialog ([^error.png]) with the following error is showed:

Unable to complete your request. The following exception occurred: Unexpected HTTP response code when requesting URI 'http://localhost:8080/kie-server/services/rest/server/queries/processes/instances/5/variables/instances/myFile%20(1/1)?page=0&pageSize=100'! Error code: 404, message: RESTEASY003210: Could not find resource for full path: http://localhost:8080/kie-server/services/rest/server/queries/processes/instances/5/variables/instances/myFile%20(1/1)?page=0&pageSize=100.

So it seems like " " (single space) is correctly escaped to "%20" but "/" is not escaped to "%2F" from original {varName} = "myFile (1/1)".

This is a simple reproducer bpmn file: [^BusinessProcess.bpmn]