Sometime during the 2.6 release of Moodle, the "course_modinfo" class in "/lib/modinfo.php" had many of its properties changed from "public" to "private". Prior to that, it was common for modules to directly access the "groups" property in the "[modname]_get_recent_mod_activity". During 2.6, the "private" change meant that code could no longer directly access the "groups" property, and the "[modname]_get_recent_mod_activity" was rewritten. This function was never updated in questionnaire and needs to be done.

Reference from forum module:
2.5 - https://github.com/mchurchward/moodle/blob/MOODLE_25_STABLE/mod/forum/lib.php#L5970
2.6 - https://github.com/mchurchward/moodle/blob/MOODLE_26_STABLE/mod/forum/lib.php#L6078