I just imported your library into Salesforce.com (to be clear: dhtmlxgantt_csp.js AFTER dhtmlxgantt.js) and tried it in a lightning component, but get this error:
“Uncaught AuraFriendlyError: Custom Script Eval error [SecureDOMEvent: [object Event]{ key: {“namespace”:“c”} }]”
This error is Salesforce related. They have something called ‘Locker Service’ that prevents several libraries out there to not work on their platform.
I realize you are not Salesforce experts, and I don’t expect you to be, but am happy to help if you are willing to address the issue. Please let me know what you need (access, steps to reproduce, share screen, phone call etc).