webform add more module does not show add more button
It seems the module has no good support and does not work properly with latest versions of webform I think both 3 and 4 versions

Here is the issue that describes the problem you are having and I am posting this as a solution as there is numerous workarounds there that might give you a solution and some patches to try but none were tested by me.

If admins say this is not fit for an answer I will erase.