Restarting iPhone SE removes custom Control Center items

On my iPhone SE, currently running iOS 26.2.1 (but also multiple previous versions), restarting the phone will remove all custom items from the Control Center. The blank boxes showing that 'something was here' remain.

Before I finally gave up the headphone jack on my iPhone 6, I assumed it was a glitch because I was on old hardware. But now that I've upgraded, the problem remains.