Cannot edit Document Template of Library

Question

today I tried to change my custom Document Template for one of my Sharepoint Librarys.
(So everytime someone click on new Excel File, he opens this template)
Unfortunately its not longer possible to modify the file, when I klick the Edit Button nothings happening. Problems occur on both Edge and IE, but the IE throws the following Error:

Currently i am using IE 11 so that should be no problem.

Before writing this post I checked that I am still Owner of the Page.
All other Files can be open in the Browser like expected, the problem occurs only when editing a template file

Here in Edge when I try to click the Link nothings happening

EDIT I encountered another unexpected behaviour. When I click on the [Edit Template] Buttons nothings happening, but when I right click and "Open in new Tab" the file isn't opened but downloaded as a copy which isn't connected to Sharepoint

Answer 1

Have you tried using Add template option shown below?

You can refer to this article Many ways to use document templates

Answer 2

Please check if the URL of the template is right or re-upload the document template

1.Sign in the site collection as an admin

2.Go to Site settings page >> click on Site conent types under the Web Designer Galleries

3.Go to the Site Content Types page, click the Document content type

4.Click on Advanced settings

• On the "Enter the URL of an existing document template" textbox to check the template URL is right
• Then, please select the "Upload a new document template" checkbox, and upload this template again