The same thing was happening to me. I removed the files from "C:\Users\USERNAME\.leonardo\" so it would re-download and I am still missing the data, 6 hour chart shows nothing. 12 hour and 1 day shows flat lines and then nothing for the period. All currencies have the same issue. Longer time spans work without issue.

Oddly, I had the correct data in those blank areas all day until I restarted Leo.