Question

I installed the app but then I changed my theme. I've uninstalled and tried to reinstall but it just gets stuck on the loading page "Please allow us a moment to load templates, products, collections, pages, and blogs."

Answer 1

The quick answer is to delete the file at snippets/null.txt and the new sections will automatically be converted.

Auto conversion of sections is new a new feature and we haven't run into this situation yet.   Heres what happened:

1.  Your theme is not installed directly from the Shopify App store, the theme store ID of your theme is null.
2.  When we see a null theme store ID, we don't know what theme you have
3.  We auto-convert your themes sections. 
4.  We place a blank file named (theme_store_id).txt in your snippets folder to indicate sections have been installed
5.  New sections are not being installed because you already have a null.txt file

Comments

This answer doesn't really make sense because it doesn't explain getting stuck.   It sounds  more like an error in the converter.

Answer 2

Heres what happened:

1.  Your theme is not installed directly from the Shopify App store, the theme store ID of your theme is null.
2.  When we see a null theme store ID, we don't know what theme you have
3.  We auto-convert your themes sections. 
​
There must've been some kind of error when converting those sections or it was taking a really long time.