Update:
I deleted all audio devices and removed the audio tracks from the one sequencer that included them, then force deleted all imported audio files, saved, restarted UEFN, and still am unable to move beyond this error.
To the best of my memory, this day of working on the island primarily involved placing hundreds of assets such as rocks and trees, adding some torches, a few terrain paint touch-ups, adding accolade and analytic devices, adding more collectible coins, and messing with a day sequence device to get it closer to working properly.
All assets and devices in this map are original to UEFN and have not given me issues in the past.