Limit the php explode to 2 to prevent extra '=' sign content in the attribute value being explode to more than 2 element in result array.

--UPDATE-- add space after comma ','

Author: Duong Hoang

app/code/Magento/ConfigurableImportExport/Model/Import/Product/Type/Configurable.php

@@ -573,7 +573,7 @@ protected function _parseVariations($rowData)
 
             $fieldAndValuePairs = [];
             foreach ($fieldAndValuePairsText as $nameAndValue) {
-                $nameAndValue = explode(ImportProduct::PAIR_NAME_VALUE_SEPARATOR, $nameAndValue,2);
+                $nameAndValue = explode(ImportProduct::PAIR_NAME_VALUE_SEPARATOR, $nameAndValue, 2);
                 if (!empty($nameAndValue)) {
                     $value = isset($nameAndValue[1]) ? trim($nameAndValue[1]) : '';
                     // Ignoring field names' case.