It's working now. Seems the issue was at my end. I used the wrong field type. Disabling auto actions didn't make any difference.

I used [cb_corp_feepaid] instead of [cb:userfield field="cb_corp_feepaid" /] as below:

[cb:if usergroup !includes "12"][cb_feepaid][/cb:if][cb:if usergroup includes "12"]£[cb:userfield field="cb_corp_feepaid" /][/cb:if]

Thanks