I used to be able to export the information from the chart on My Plan. Is there a way to export or download the historical data?

To the best of my knowledge, the only chart that can be exported is the Daily Entry .. https://forum.lowcarber.org/myplan.php?&do=entry ... which can go directly into your forum journal, or be saved as a BB code or html document. To save historical data, you'd have to select the desired date from the drop menu at the top of the chart. I don't think there's any way to export multiple days at once, only one day at a time.