Edit: the following fixed the problem temporariky, but a few hours later, it's back again. I'm leaving this up in case it helps someone figure out the real issue. --- You need to update and reload your Theme to fix this problem. (Note: if you are running a theme that has not been updated by the developer since last July, this may not work for you.) Go to Settings > Wallpapers and Themes. Tap the hamburger icon in the top left, then tap My Stuff. If "Update All" appears, do that first. Then tap your theme, followed by Apply. After living with this issue for almost 9 months, this is what finally fixed it for me. Hope it works for you too.
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