Tankers bearing sanctioned Russian liquefied natural gas (LNG)
IIRC, you have to burn off a certain percentage each day to keep LNG on a tanker cool, so presumably, they're going through their LNG supply.
kagis
https://www.quora.com/What-is-a-boil-off-gas-in-LNG
Despite LNG tanks being insulated due to natural evaporation and rolling of liquid due to sea conditions there is about 0.10 - 0.15 % of total amount of cargo evaporating daily.
I'm sure they burn it off. I can see some reference to LNG tankers having the ability to use the LNG as fuel,, so I assume that they just send it there.