It makes sense if you look at how they are doing it.
Russia can't get in its own agents in any more and, as widely reported, are recruiting third parties via the internet - crooks, opportunist, idiots to pay to do it on their behalf.
To build networks they need to start off getting them involved doing minor sabotage and committed since the Russians now have proof of their treason. Those that prove competent they can provide with caches of explosives etc and have available for when they are required.
Minor sabotage such as cutting the fibre-optic cable is just a weeding/training assessment exercise on behalf the FSB.