The app has a maximum of 1.500 chords on iOS/iPad and 1.650 chords on macOS. Repeats of lines and parts included.
Under the hood, the app is working with MIDI files. Creating large MIDI files with too many chords is leading to performance issues. To illustrate this: Such files usually have a duration of more than 45 minutes which the app does not support.
That's why you might see a warning when creating songs with lots of repeats.
Try to reduce repeats of parts and lines. If possible, use the "loop song" feature for practicing chord progressions in a loop.