Cannot import CreateAI hex to MakeCode

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Reproduction steps

1. Import the following data samples .json file to a new session: 238-samples-cannot.json
2. Click on "Train" button.
3. Save hex file.
4. Import saved hex file.

Error message from console

pxtapp.js:1 SyntaxError: Unexpected non-whitespace character after JSON at position 3 (line 1 column 4)
    at JSON.parse (<anonymous>)
    at pxtapp.js:1:150106
warning: Sorry, we could not recognize this file.

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I suspected it was due to the large number of data samples, but having tried it with the following data samples json, which also includes 238 data samples (238-samples-2.json), it doesn't seem to be the case.