Hi Gyorgy,
Thanks for using Syncfusion products.
We need the below additional details regarding the reported issue so that we could provide you solution as soon as possible.
1. Server-side code snippets where you generate template
2. Client-side code snippets where you add template to grid
3. Html string output of template generated from server-side
4. Grid Code snippets
5. Essential Studio Product version details
Also, the general suspect on this issue is that the some additional elements were generated in server-side or client-side before adding the template to grid. So please ensure before adding the template to grid that it has correct values.
Regards,
Alan Sangeeth S