Looker Studio - Custom fields not saving, but no error?!?!

Starting this afternoon, I am experiencing a very frustrating situation where I cannot save a custom field. I complete the steps to "add a group" successfully seven times. The eighth time? Click save, and nothing. No error messages, but no "field saved" confirmation. Looking at the network in Chrome dev tools, clicking the save button does not result in the expected POST request to save the variable. Hard reload + clear cache, restart, incognito browser all didn't work. Any ideas? I tried another account and different report - same thing.

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