magento2: 2.1.3 CE - Unable to set attribute set for new product (possibly data-migration issue)

Preconditions

1. Magento 2.1.3 CE (from Composer)
2. PHP v7.0.14 Apache

This was a 2.1.2 install which was then upgraded to 2.1.3 before any products/attributes were setup. Products/attributes were imported from 1.7.0.2 using the data-migration-tool.

Steps to reproduce

1. Create an attribute set (I’m using some imported from Magento 1.7)
2. Go to Products->Catalog and Select “Add Product” and Simple Product (Configurable Product also fails, not tested another). URL is currently https://XXXX/catalog/product/new/set/21/type/simple/key/KEY/
3. Change the “Attribute Set” dropdown from Default to anything else. A POST call is made to: https://XXXX/admin/catalog/product/reload/type/simple/store/0/popup/1/componentJson/1/prev_set_id/21/key/KEY/?set=15&isAjax=true [post data includes a form_key and returns 181Kb of JSON] another POST is made to: https://XXXX/admin/catalog/product/reload/type/simple/store/0/popup/1/componentJson/1/prev_set_id/15/key/KEY/?set=undefined&isAjax=true which fails with a 503 Service Unavailable code [post data includes a form_key and returns a standard “There has been an error processing your request” with the corresponding var/report file containing:

a:4:{i:0;s:37:"attribute_set_id is a required field.";i:1;s:4163:"#0 /WEBROOT/vendor/magento/module-eav/Model/Attribute/GroupRepository.php(111): Magento\Framework\Exception\InputException::requiredField('attribute_set_i...')
#1 /WEBROOT/vendor/magento/module-catalog/Model/ProductAttributeGroupRepository.php(57): Magento\Eav\Model\Attribute\GroupRepository->getList(Object(Magento\Framework\Api\SearchCriteria))
#2 /WEBROOT/vendor/magento/module-catalog/Ui/DataProvider/Product/Form/Modifier/Eav.php(426): Magento\Catalog\Model\ProductAttributeGroupRepository->getList(Object(Magento\Framework\Api\SearchCriteria))
#3 /WEBROOT/vendor/magento/module-catalog/Ui/DataProvider/Product/Form/Modifier/Eav.php(241): Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\Eav->getGroups()
#4 /WEBROOT/vendor/magento/module-catalog/Ui/DataProvider/Product/Form/ProductDataProvider.php(68): Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\Eav->modifyMeta(Array)
#5 /WEBROOT/vendor/magento/framework/View/Element/UiComponentFactory.php(269): Magento\Catalog\Ui\DataProvider\Product\Form\ProductDataProvider->getMeta()
#6 /WEBROOT/vendor/magento/framework/View/Element/UiComponentFactory.php(164): Magento\Framework\View\Element\UiComponentFactory->mergeMetadata('product_form', Array, false)
#7 /WEBROOT/vendor/magento/framework/View/Layout/Generator/UiComponent.php(124): Magento\Framework\View\Element\UiComponentFactory->create('product_form', NULL, Array)
#8 /WEBROOT/vendor/magento/framework/View/Layout/Generator/UiComponent.php(93): Magento\Framework\View\Layout\Generator\UiComponent->generateComponent(Object(Magento\Framework\View\Layout\Data\Structure), 'product_form', Array, Object(Magento\Framework\View\Layout\Interceptor))
#9 /WEBROOT/vendor/magento/framework/View/Layout/GeneratorPool.php(86): Magento\Framework\View\Layout\Generator\UiComponent->process(Object(Magento\Framework\View\Layout\Reader\Context), Object(Magento\Framework\View\Layout\Generator\Context))
#10 /WEBROOT/vendor/magento/framework/View/Layout.php(327): Magento\Framework\View\Layout\GeneratorPool->process(Object(Magento\Framework\View\Layout\Reader\Context), Object(Magento\Framework\View\Layout\Generator\Context))
#11 /WEBROOT/var/generation/Magento/Framework/View/Layout/Interceptor.php(89): Magento\Framework\View\Layout->generateElements()
#12 /WEBROOT/vendor/magento/framework/View/Layout/Builder.php(129): Magento\Framework\View\Layout\Interceptor->generateElements()
#13 /WEBROOT/vendor/magento/framework/View/Layout/Builder.php(65): Magento\Framework\View\Layout\Builder->generateLayoutBlocks()
#14 /WEBROOT/vendor/magento/framework/View/Layout.php(244): Magento\Framework\View\Layout\Builder->build()
#15 /WEBROOT/vendor/magento/framework/View/Layout.php(935): Magento\Framework\View\Layout->build()
#16 /WEBROOT/var/generation/Magento/Framework/View/Layout/Interceptor.php(492): Magento\Framework\View\Layout->getOutput()
#17 /WEBROOT/vendor/magento/framework/View/Result/Layout.php(181): Magento\Framework\View\Layout\Interceptor->getOutput()
#18 /WEBROOT/vendor/magento/framework/View/Result/Layout.php(164): Magento\Framework\View\Result\Layout->render(Object(Magento\Framework\App\Response\Http\Interceptor))
#19 /WEBROOT/var/generation/Magento/Framework/View/Result/Layout/Interceptor.php(89): Magento\Framework\View\Result\Layout->renderResult(Object(Magento\Framework\App\Response\Http\Interceptor))
#20 /WEBROOT/vendor/magento/framework/App/Http.php(139): Magento\Framework\View\Result\Layout\Interceptor->renderResult(Object(Magento\Framework\App\Response\Http\Interceptor))
#21 /WEBROOT/vendor/magento/framework/App/Bootstrap.php(258): Magento\Framework\App\Http->launch()
#22 /WEBROOT/index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http))
#23 {main}";s:3:"url";s:192:"/XXXX/catalog/product/reload/type/configurable/store/0/popup/1/componentJson/1/prev_set_id/16/key/9b342c123e56ef9b1123af9d7cc8711bb6206efb3f693d9f74d1028b926d8834/?set=undefined&isAjax=true";s:11:"script_name";s:10:"/index.php";}

another POST is made to: https://XXXX/admin/catalog/product/reload/type/simple/store/0/popup/1/componentJson/1/prev_set_id/15/key/KEY/?set=&isAjax=true which fails with a 404 Forbidden code (and HTML is returned)

Expected result

1. The list of attributes is updated

Actual result

1. The “Please wait” spinner continues to show.