A frequent issue if you are using a really old phone. Happened very frequently on my Nokia Lumia 625 (512 MB RAM) running Windows 10 creators update (yeah, I got it by registry tweaks). If the scenario is same for you, I have a fix: (but will need really special techniques of knowing registry editing)
First try doing a soft-reset (hold power and volume up button simultaneously for 10 seconds)
Follow these articles: Enable Dynamic page file... MGz processor and memory increase...
You will need to know your maximum processor speed and RAM from any specifications list available online. If you need help on these do tell me. This will most probably fix the issue as it did on my Lumia. Not only the loading page problem will be gone, but your phone will also become faster.