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This error can occur if the import process is interrupted, Ryan.
We can do browser troubleshooting steps to get rid of any cache-related issues.
Using a private browser can be a good start since it doesn't store cache files. Using other supported browsers can be a good alternative, too. Because each browser users different sets of cache files.
Then, try importing your vendors again. If you can successfully do it, you can clear the cache storage of your regular browser.
Otherwise, I'd recommend reaching out to our QuickBooks Customer Care Team. They'll be able to investigate and provide further troubleshooting steps to get through this error.
I'll be right here if you have other concerns.