Bug or Resource limit?

I have an admittedly very complex query in BigQuery, which I am pasting in the Custom Query data source of Looker Studio.

This has been working well for weeks, but suddenly I am unable to successfully duplicate an existing, working data source and "reconnect". I get the standard "Sorry, we encountered an error..." without any error code message.

The strange thing, is that when I look in my BigQuery logs, I can see the looker-studio request, and the results do successfully process and publish. But yet, I still get the error message.

Is this a bug, or are there some hidden resource limits or quotas that I am missing?

Appreciate any help or advice available.

Thanks

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