I want to start by apologizing for the delay in getting back to you on this issue. We have been working all hands on deck to address this issue and a few related issues in order to make sure that our bulk import APIs are working properly.
Fortunately, I can report that this issue with Custom Fields not importing properly has been resolved! If for any reason you are still experiencing issues with this, please let us know and we will look into it for you ASAP.
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