Hi Michael,
Greetings from Syncfusion Support.
We have reviewed your query,
and it appears that the limitation you encountered is related to the maximum
value of the int data type. we recommend using the long data type for
the Id field in your Gantt chart.
We have prepared a sample
where the Id field is defined as a long data type and attached it
below. Additionally, we have also included a sample with the Id field
defined as an int data type and attached it for comparison. The outputs
of both samples are provided as well.
Long Data Type:

Int Max Value:

Sample Link: https://www.syncfusion.com/downloads/support/directtrac/general/ze/LongType1333831991
However, we understand
that you are still facing the issue. To investigate further, we request you to
share more information to find the cause of the issue.
1.
Please confirm whether you have clear bin and obj to avoid conflicts while
upgrading the project.
2. Environment where the application is running.
3. Specific scenario you have faced the issue(Video demo)
4. If possible replicate the issue in shared sample and revert us back.
Once we receive this
information, we will be better equipped to identify the root cause of the issue
and provide you with the necessary assistance.
Thank you for choosing
our services.
Regards,
Ajithkumar G