Groups stopped working after upgrade to 29.0
As an update I noticed the data in the "users_user" table was inconsistent with legacy rows in the table having null values in some of the columns and rows created since the update to 29.0 having only zero or empty columns rather than null. So I ran the below two queries to bring the data consistent. This did not fix the problem, but I felt it reporting all the same:
update users_groups set usersTrackerId = 0, groupTrackerId = 0, usersFieldId = 0,
groupFieldId = 0, registrationUsersFieldIds = "", userChoice = "" where usersTrackerId is null;
update users_groups set Anniversary = "", prorateinterval = "" where Anniversary is null;