Seedless blueberry jam - consistency
Blueberries are generally low-pectin fruits, so many jam recipes and jam making guides specifically call for adding pectin. That said, some do not - but these use the whole pureed fruit. When you filter out the seeds and skin, you remove much of what pectin there is in blueberries naturally, leaving you with runny jam.

The solution, then, is to add pectin or some other fruit that contains some.

As a note, unripe fruit, including blueberries, often has more pectin than ripe, but if you're using frozen blueberries, they're likely to be picked at their peak and rather low in pectin.