Why AAL not shortable

Trying to make a short sell of AAL in the Paper Trading account, but got the error of “asset AAL cannot be sold short”. The asset info for AAL seems to indicate it should be shortable:

In [19]: api.get_asset(‘AAL’)
Asset({ ‘class’: ‘us_equity’,
‘easy_to_borrow’: True,
‘exchange’: ‘NASDAQ’,
‘id’: ‘41b54729-8470-4593-be38-b3a681871f81’,
‘marginable’: True,
‘name’: ‘American Airlines Group Inc. Common Stock’,
‘shortable’: True,
‘status’: ‘active’,
‘symbol’: ‘AAL’,
‘tradable’: True})

Are there any other settings or limitations that could disable this short sell? I have successfully made short bracket order on another symbol though.