Thank you for details provided, I see the problem. Here is a link to track the status https://github.com/bryntum/support/issues/5512
As a workaround, try to add durationUnit
field in your data. https://bryntum.com/docs/gantt/api/Gantt/model/TaskModel#field-durationUnit
Support Forum
It's by design. The timeline initially has startDate and endDate.
https://bryntum.com/docs/gantt/api/Gantt/view/Gantt#config-startDate
https://bryntum.com/docs/gantt/api/Gantt/view/Gantt#config-endDate
If omitted, it will be calculated.
To have it adjusted, enable https://bryntum.com/docs/gantt/api/Scheduler/view/mixin/TimelineScroll#config-infiniteScroll
const ganttConfig = {
infiniteScroll : true,
project: {
All the best,
Alex