I have version 1.7.8.11 and I cannot select carriers in the payment preferences, they appear with a double dash instead of the checkbox.
I have uninstalled the carriers several times and reinstalled them but there is no way. I also don't see the difference between 31, which has the visible checkboxes, and the others. What is the reason why the checkboxes do not appear?
I had the same bug once.
Check your DB , you probably have some problem in the ps_carrier table in relation to the link between id_carrier and id_reference for active carriers.
This causes a problem in Symfony's form generation for the affected carrier(s).