Workspace custom logo can not be changed/updated if there is an additional form attachment in the "sys_aw_master_config" form. It shows the default ServiceNow logo all the time.
1. Go to the "sys_aw_master_config" table and open the "Agent Workspace" record.
2. Upload a custom logo via the Custom logo field.
3. Open the "Agent Workspace" to ensure that the logo is changed.
4. Go back to the same sys_aw_master_config record of the "Agent Workspace" and attach a file to the form. The file could be an image or any other documents.
5. Open the Agent Workspace again to check the logo. The custom logo is replaced with the default ServiceNow logo if the form has an attachment.
This is expected behaviour. Updating the logo is only possible without any other attachment for the master config table.