This is coolbert:
That recent Swedish episode of "submarine hysteria" does have a context? As not reported elsewhere.
"Sweden’s Mysterious Submarine Hunt and Its Significance for Nordic-Baltic Security"
"The Swedish ASW operation comes right after the end of the multinational naval exercise Northern Archer, where Swedish, Danish, Polish, and Dutch frigates, submarines, and jets practiced, among other things, how to combat a submarine threat. It is not far-fetched to think that the Russian submarine infiltrated into Swedish waters to observe the exercise, record ship signatures, and study the capabilities of the participating units."
These type of things do not exist in a vacuum and surely Northern Archer was a catalyst for renewed and more vigorous Russian naval reconnaissance in the Baltic.
Without Northern Archer a Russian submarine incursion of Swedish waters appears strange indeed, within the context of the military exercise not so strange but to be expected.