"Invalid day index' error after upgrading


I got this error after upgrading from “Version 7.0.11, Professional Edition” to “Version 7.1.7, Professional Edition”. Any idea how to fix this ?

Here is a sample date > 2021-11-16T00:00:00 I loaded

Thanks !


That issue can occur if you have the wrong date format. According to the screenshot, you try to do something inside the tooltip_text template, probably converting the date, but instead of providing a variable with the Date type, there is something else.

However, it is hard to suggest what might be wrong as I don’t see your code.
Please, add your configuration in the following snippet and make sure that the issue is reproduced there:


Then, click on the Share button and send me the link.

Or send me a ready demo with all the necessary Javascript and CSS files so that I can reproduce the issue locally.


hi, thanks for the response. I really appreciate it.

gantt.config.deepcopy_on_parse = true
fixes the issue.