I tested the patch proposed on #37661 on Windows Phone 10 with the Edge browser. Here’s a visual record of that experience:
Open the customizer, tap “change.”
Tap “see 10 themes.”
Scroll through the themes.
Tap a theme screenshot.
Tap the right arrow.
Tap the close icon.
Tap “Filter themes.”
Tap “featured.”
Tap “See 15 themes.”
Should this have scrolled back to the top instead of starting down the page? Scroll to top.
Tap “Filter themes.”
Tap Favorites.
Tap the username input.
Enter username, tap get favorites.
Tap see 12 themes.
Tap filter themes.
Tap feature filter.
Scroll through list, tap on some features.
Tap see 294 themes.
Tap theme screenshot.
Tap install.
Installing… tap close icon.
Installed. Tap Filter themes.
Scroll up.
Tap search input.
Enter a search, tap see 7 themes.
Scroll.
Tap live preview.
Loading…
Tap preview.
The biggest potential fixes I found were to show a loading indicator in the filters (next to the theme count button in the header?) when a new filter is loading, and to scroll the themes container to the top whenever a new section is opened or a search/filter is changed (which should be happening, but isn’t).
I should also note that since it is impossible to reorder images in galleries with Chrome on laptops that support touch, see #31652, I had to go to the text editor to fix one that jumped out of order when creating this post.