The MLD implementation did not follow the RFC correctly when it is the Querier. The Querier should use a general query and get query messages from all members of all groups. This would be driven by a single timer per sub-nset since all groups are queried at once. Instead, the design used a Multicast Address Specific Query with one timer per group and ignores groups that we are not members of.
Similary, the MLDv1 compatibility timer should be a single, separate timer, not a per-group timer.
net/mld: Group may be NULL when sending a general query
8a3fc26b74