Currently original images will only be hidden, but still present in the markup. So they will be loaded (if the loading attribute ist not set to 'lazy'). The images should not printed at all in this case, only the empty photoswipe links are required.
Maybe related to 🐛 After update to 4.0.1 - Photoswipe responsive formatter "Override first image thumbnail style" isn't respected. Active ?!
1. Configure the photoswipe formatter on a multi value media image reference field like this:
2. Check the markup in the frontend:
The Photoswipe responsive formatter has kind of the same problem, but is missing the src attribute:
Active
5.0
Code
Ok, test failure is actually valid but unrelated, I will create a follow-up issue for that.
RTBC!
Never mind, the test was incorrect after all. I added the test changes to 5.x dev.