Adding multiple single user picker fields to customer portal causes some fields to not be editable

Issue Summary

Users are unable to edit some user picker fields in the customer portal when multiple user picker fields are present.

Steps to Reproduce

1. Create 3 or more custom fields of type User Picker (single user)
2. Add these fields to the customer portal (Project settings > Request Types)
3. Load the customer portal

Expected Results

All user picker fields are editable

Actual Results

Not all user picker fields are editable. Some will only show the label and the drop down will be missing.

The following error is also visible on the browser's console:
 

batch.js?locale=en-BR:2186 Uncaught TypeError: Cannot read properties of undefined (reading 'split')
    at Object.created (batch.js?locale=en-BR:2186:20460)
    at l (batch.js?locale=en-BR:768:370)
    at c (batch.js?locale=en-BR:769:40)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)
    at c (batch.js?locale=en-BR:769:199)

Workaround

Replacing servicedesk-frontend-plugin jar file via plugin directory.

• If JSM was installed as the first application, the directory would be: 
  • atlassian-jira/WEB-INF/application-installation/jira-servicedesk-application
• If JSM was installed as the 2nd application, using obr, the directory would be:
  • <shared-home>/plugins/installed-plugins

Steps

Prepare Jira 8.20.5/4.20.5 installation:

1. Go to atlassian-jira/WEB-INF/application-installation/jira-servicedesk-application or <shared-home>/plugins/installed-plugins (see the points above)
2. Copy servicedesk-frontend-plugin-4.20.5-REL-0003.jar

On Jira 8.20.6/4.20.6 installation > go to the same directory

1. Stop Jira on all nodes
2. Remove servicedesk-frontend-plugin-4.20.6-REL-0005.jar
3. Add servicedesk-frontend-plugin-4.20.5-REL-0003.jar
4. Start Jira and perform a full reindexing

 
If it's atlassian-jira/WEB-INF/application-installation/jira-servicedesk-application directory, then apply this on all nodes. However, if it's <shared-home>/plugins/installed-plugins, then just apply it once in the shared-home directory.

Remember to perform this in the staging instance first, before applying it in the production.