The Redmine Gantt chart shows only up to 500 issues and versions
By default, the maximum number of items such as issues and versions shown on the Redmine Gantt chart is 500. When the number exceeds this limit, the message "The chart was truncated because it exceeds the maximum number of items that can be displayed (500)" is shown, and only 500 items are shown.
To raise the number of items that are shown, change the setting "Maximum number of items displayed on the gantt chart" on the "Administration" → "Settings" → "Issue tracking" screen.

