welcome to the Atlassian Community!
Unfortunately, it will be impossible to tell without getting more information about your deployment and how you use Confluence.
Assuming you are using Confluence Cloud there are reports in the past about missing pictures, like: https://community.atlassian.com/t5/Confluence-questions/Some-images-are-not-displayed-in-Confluence-Page/qaq-p/2035469
They were directed to Atlassian Support - so in case you haven't done yet, it could be an idea to raise a support request on that.
Regards,
Daniel
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