If these communes are unstable enough they generate piracy, wouldn't they also be unstable enough to try to spread revolution to neighboring countries making north finland a serious security threat for the Swedish kingdom*?

After all, while denmark and the baltic sea acts as a buffer state between the prussians and Sweden, Sweden is sharing borders with a communist nation that is unstable and threatens naval activity in the region.

Needless to say, half of finland isn't enough to contain communism in the region.
Chances are spain will want other allies in the region, which is where Sweden would come in.  After all, you have not only the northern finland communes, but also the st. petersburg communes that share the baltic sea with Finland and sweden.

The presence of chinese subs most certainly not helping a thing.

*Can't call it a empire unless they take over finland and parts of norway again.