Signing window disappears in Adobe Acrobat Pro when requesting signatures on a .pdf

When i have a .pdf document open in Adobe Acrobat Pro, and I go to request a client signature normally another window pops up where I enter in the clients email address and a short message. I often have the following problem, where this window appears fom maybe half a second, and then disappears.

Normally to fix this, I have to sign out - then sign back in again. But ocassionally this does not work and the only way to fix it is to do a shutdown and restart.

Does anybody know what is going on here and how to fix this problem