Sophia here from Shopify. Welcome to the Shopify Community!
The error message indicating a page took too long to load can sometimes be a local network issue. In that case, you can check in with your internet service provider to see if they're having any issues with accessing Shopify.
I noticed that the URL you're navigating to is "app.shopify.com/services/login", so using a different login URL might help. Did you get to this link through https://accounts.shopify.com/store-login or by adding
/admin to the end of your .myshopify.com URL or domain? Let me know if either of those options work for you. You can also try clearing the cache for a longer period of time if possible: