Hi Ivan,
Thanks for contacting Syncfusion Support.
We have checked with your query “Problem in rendering groupbutton control in _layout.cshtml shared page” and tried in a local sample, but couldn’t reproduce the reported issue at our end. We suspect that the issue may occur because the required scripts and CSS files may not have referred properly. So, please ensure that all the required scripts and the CSS files are referred properly in your application.
For your convenience, we have created a simple sample based on your requirement and attached in the below link. Please check it.
If the issue persists, then please revert with an issue reproducing sample (if possible) along with the below mentioned details so that we can provide exact solution for your requirement.
1. Essential Studio version.
2. Console errors. (if any)
Regards,
Prem Kumar. M