iPad Pro 12.9” gen1 iOS 13.3.1
Issue also occurs on iPhone 6S running iOS 13.3 and Joplin 10.0.45.
When opening the sandwich menu the dark part of the bar aligns with the slide-in menu, and the white part aligns perfectly with the part of the note which is still visible. Hopefully this is useful.
Both of the above pictures are when viewing the note list - once a note is opened, the black and white bar on the top inverts:
iPhone XS Max
Same issue on iOS 13 and iPadOS 12 for the last six weeks or so