I think issue you are encountering was caused by an incident with Amazon Web servers, which had failures with their DNS causing attachments stored in AWS to fail in Trello.
If you're still not seeing them, you may need to flush your DNS cache first which you can do by following the procedure described in https://www.a2hosting.com/kb/getting-started-guide/internet-and-networking/clearing-the-dns-cache-on-your-computer#Google-Chrome-browser.
If after flushing your DNS cache, you're still unable to view your images and avatars, you'll need to change your DNS settings on your machine and use another DNS server that is no longer impacted by this issue, such as Google DNS (126.96.36.199 and 188.8.131.52). Depending on your OS, you will need to do this from your Network system settings (see https://www.windowscentral.com/how-change-your-pcs-dns-settings-windows-10 for Windows and http://www.macinstruct.com/node/434 for macOS, it's an old one but still relevant).
If you had to thrive a new habit during a lockdown, what would it be? Trello
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