I just the same problem on SS3.1 with the latest master version of Userforms from Github (today). The Form tab in the CMS was showing up blank.
I did a flush on the actual page in the CMS and it returned. eg. /admin/pages/edit/show/3?flush=1
A normal flush on /admin wasn't enough, it had to be on the actual/specific page.
Now I have a similar problem with SS 3.1.12 and Userforms. I think I flushed what can be flushed, but I can't add a form.
The tabs are there and when I try to add any type of field nothing happens. I click on the button, but it doesn't work. Anyone has these problem and maybe could solve it.
@Dobby, it shouldn't look like that. That indicates you're missing css or js files. Ensure the folder is called 'userforms' not 'silverstripe-userforms' and then try disabling combined files through Requirements