UIWorkIntervalTiming workIntervalStart
I can observe the same issue with a UICollectionView and UITableView. I suspect it is a diagnostic output used to analyse the scrolling performance.
Note: I notice this issue from Xcode 10.2
in UICollectionView if you swapping too much faster than collection getting Freeze for few moment on Simulator but Real Device working fine.
Earlier Xcode version this features is UIWorkIntervalTiming had its logging privileges revoked