It appears that Russia has figured out a secondary function for their grey fleet: Hybrid warfare.
They create a "shipping company" to some country outside of the sanctions. The company likely has only a single asset: the vessel itself. The vessels are very old and in poor condition and have no insurance. A crew is hired to operate the vessel.
Normally these vessel are used to circumvent the sanctions in place, for example to sell Russian oil.
As a recent new development it appears that these vessels are also used to perform hybrid operations that target undersea cables. Prime example is the Baltic sea that is relatively shallow, and the cable locations are well documented. There has been multiple recent incidents involving ships that "accidentally" drag their anchors and cause damage.
The operation likely also involves finding crew members willing to take a compensation for performing the malicious task of dragging the anchor on the seabed. This is made easier by the fact that the crew can claim ignorance or bad seamanship. The threat to these persons is very limited, as the Nordic countries have very lenient legal systems. It is unlikely that they would be incarcerated for a significant amount of time, even if found guilty of sabotage.
The payout vs the investment is significant. The damage caused by the disruption of the undersea #telecommunications and electricity cables likely far exceeds the value of the ship or the cargo combined. The involved ship can just ignore any requests to stop or allow for inspections, as long as they are in international waters.
Considering there is a really high barrier in disrupting international shipping, anyone willing to abuse the system can continue to do so until significant changes will be made.