We are unable to reproduce the above reported issue. We suspect that script and CSS necessary for EJ components might have not loaded properly. We have created a sample sharepoint farm solution in which EJ button control and the script file “ej.widgets.all.min.js” are added. Could you please check with it?
Sample Location: Sharepoint 2013 sample
If you are using web components alone in the project means, instead of ej.widgets.all.min.js you could use ej.web.all.js file and check whether the issue occurs or not. Please refer the following knowledge base document to know the difference between the script files
If still you face difficulties, kindly get back to us with more information about your issue and we will happy to help you.