Captcha cannot be solved (there are no letters) when users visits the form for the first time after logout.

Steps to reproduce:
1. Login as admin
2. Create new form with Captcha and Button
3. Publish it
4. Logout everywhere
5. Go to yourdomain.com/login
6. Login as admin
7. Go to your form on frontend
8. Go to yourdomain.com/logout
9. Go to your form on frontend

Expected:
Solveable captcha is presented

Actual:
Captcha without letters is presented (see screenshots).