Do you have a fancy custom loading animation instead of an UIActivityIndicatorView? You may want to check if it has an accessibility label so a VoiceOver user knows that something is happening. Something like "In progress" or "Loading" could work.
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Even when setting a view as modal for accessibility, you may notice that VoiceOver's focus stays in the same place, instead of moving to the presented view. You can post a screen changed notification and pass the view that should get the focus.

When using Voice Control, say: "Show names". You'll see all the accessibility labels for interactive elements overlaid on the screen. It will help you identify labels that can be improved, or actually missing. Labels are not just for VoiceOver.
@azzoor has this great video with some advice on how to set up your device for testing accessibility and a ton of tips will get you testing effectively in no time. https://m.youtube.com/watch?v=Ca1H6wF348g&feature=youtu.be
Content © Daniel Devesa Derksen-Staats on Accessibility up to 11! is licensed under CC BY 4.0. License details