For example:
form.getItem(‘btnRefresh’).hide();
Error - undefined hide property.
Unfortunately I was not able top reproduce your issue locally.
The following snippet works well:
https://snippet.dhtmlx.com/666iyni3
If the problem still occurs for you please, provide a code snippet, complete demo or a demo link, where the problem can be reconstructed locally