MySQL slow query with IN() clause on indexed column
You may try a temporary table and join against that:

create temporary table t1 
( type varchar(255) not null
);

insert into t1 (type) values ('Namespace.Domain.User.Event.SomeEvent1Happened');
insert into t1 (type) values ('Namespace.Domain.User.Event.SomeEvent2Happened');
insert into t1 (type) values ('Namespace.Domain.User.Event.SomeEvent3Happened');
...

create index x1 on t1 (type);

SELECT COUNT(id) 
FROM events e 
JOIN t1
    ON e.type = t1.type;