Product collection created on Shopify got missing on our app.

[DSers]

Hi All !

We are Shopify partner running an app that can manage products imported from AliExpress and then publish to Shopify. We have a feature that can support merchant to add the product to a Collection created on Shopify when publishing to Shopify. But we are experiencing an issue that we do not have the complete list of Collection list on Shopify. Some options get missing and not synced to our app. 

Anyone has the same issue and know how to deal with it? 

Thank you in advanced.