No login after enabling altcha

Describe the issue or problem
After enabling altcha we cannot login on our journal but we would expect login to work.

Steps I took leading up to the issue

  1. Yesterday we enabled altcha on our OJS system
  2. We could work for several hours on the system, we could log in and out repeatedly, and an altcha widget was displayed next to the login fields in the UI every time we logged in
  3. Today we tried to log in again and this did not work
  4. The UI displayed the error “You must complete the validation check used to prevent spam submissions.”
  5. We disabled altcha on Log in and it was possible to log in again

What application are you using?
OJS 3.5.0-3

Additional information

Here are the settings that worked yesterday but did not work any more one day later

altcha = on
altcha_hmackey = ‘…’
altcha_on_register = on
altcha_on_login = on
altcha_on_lost_password = on
altcha_encrypt_number = 1000

I can now log in again after setting

altcha_on_login = off