The error 502 means The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.
I recommend you to check your Confluence connections. Looks like your proxy is trying to communicate to Confluence, but Confluence is too busy to reply.
These links can be useful:
Hi Community! I’m Elaine, Confluence Product Manager. You may have read my earlier post about page tree in space navigation sidebar. I'm excited to share another improvement that helps you organize ...
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