Users have updated their photo in their user profile but they do not reflect on the avatar next to their names in visual task boards

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This is due to the thumbnail file which is not found.  If you check in the browser console, you may see the following after opening https://<instance_name>.service-now.com/<sys_id>.iix?t=small compared to https://<instance_name>.service-now.com/<sys_id>.iix

One possible cause for this is a custom before insert/update business rule on the sys_attachment table.

Disable any custom before insert/update business rule.