In the recent updates, something changed about the checboxes.
Now there are 2 different types of checkbox in Evernote.
One which you can set as a list indent or the one you can add in the middle of the text.
The bad thing about the UX is the previous model for checkboxes with ctrl+shift+c has been changed to the bullet like item.
So it's no more possible to add a checkbox in the middle of the text with that short key and If you want to do that the only way is to use the drop down insert menue (the + icon) in the upper right part of the context.
If someone know that the new insert checkbox has a new short key please share it with us.