Hi Kasama,
Thank you for using Syncfusion products.
I am afraid, that I was unable to reproduce this issue. I have created a simple sample with the X axis as datetime value and zoomed it the reported issue in the Axis lines are does not appear. Could you please try to reproduce it in a simple sample and send it to us. so that we could sort out the cause of the issue and provide you a solution.
Please refer the screen shot below for your reference.
http://www.syncfusion.com/uploads/redirect.aspx?file=sshot-14_1bfcda36.zip&team=testingftpLet me know if you have any concerns.
Regards,
Jaffer.B