I've notice in the past week that there appears to be problem with images on the site, either maps or monster artwork. If I click on the image to expend it, it never loads. You simply get a with square with the loading animation. If I try to open in another tab, I get the following error:

<Error>
<Code>RequestHeaderSectionTooLarge</Code>
<Message>
Your request header section exceeds the maximum allowed size.
</Message>
<MaxSizeAllowed>8192</MaxSizeAllowed>
<RequestId>ZBTJNPWGVJ8M8YEW</RequestId>
<HostId>
EkxsEZiDg9XjwokAMwNbYJvCogt6LlZW9vVfOF8Ymy9CPKjJVH8WIqPaNvEQjSx+uigsVrREu+c=
</HostId>
</Error>

Yesterday, I notice that my avatar doesn't show anymore and I'm unable to change it.

I am having similar issues. I have tried logging out of dndbeyond and logging back in. I experience this issue on both my Android phone, and Chrome browser on Windows.

Some character icons that are selected from the dndbeyond "stock" images seem to come up, but not ones I have uploaded.

My avatar just came back but the problems with maps, artwork, and images use on character portraits still do not work.

The avatar is gone again.

Well, the problem was the browser.

For anyone having the problem just clear all site data and cookies for D&D Beyond and it should fix the issue.

It certainly fixed it for me.