All I can really tell you is that back in mid July Gazprom declared force majeure on NS1 but that one its (main) German receivers rejected the claim, while the other refused to comment on the legal angle:
Russia's Gazprom has told customers in Europe it cannot guarantee gas supplies because of "extraordinary" circumstances, according to a letter seen by Reuters, upping the ante in an economic tit-for-tat with the West over Moscow's invasion of Ukraine.
The Russian state gas monopoly said in a letter dated July 14 that it was retroactively declaring force majeure on supplies from June 14. [...]
A trading source, asking not to be identified because of the sensitivity of the issue, said the force majeure concerned supplies through Nord Stream 1.
"This sounds like a first hint that the gas supplies via NS1 will possibly not resume after the 10-day maintenance has ended," said Hans van Cleef, senior energy economist at ABN Amro.
“Depending on what ‘extraordinary’ circumstances have in mind in order to declare the force majeure, and whether these issues are technical or more political, it could mean the next step in escalation between Russia and Europe/Germany," he added.
Uniper, Germany's biggest importer of Russian gas, was among the customers that said it had received a letter, and that it had formally rejected the claim as unjustified.
RWE (RWEG.DE), Germany's largest power producer and another importer of Russian gas, also said it has received a force majeure notice.
"Please understand that we cannot comment on its details or our legal opinion," the company said.
What that means, in general:
Force majeure is a provision in a contract that frees both parties from obligation if an extraordinary event directly prevents one or both parties from performing.
FWTW, apparently, the politico-technical response from Moscow was the suggestion to open NS2, which they also said it was a German inquiry (made by former chancellor Schröder):
“Putin explained everything in detail, and the former chancellor asked if it was possible to use Nord Stream 2 in a critical situation,” Peskov said. “Putin was not the initiator, Putin did not offer to turn it on, but Putin said that it is technologically possible and this complex mechanism is ready for instant use.”
On the same day, Gazprom themselves said that getting/accepting back the NS1 turbine (the one that Scholz is photographed standing in front of) is impossible due to sanctions despite Scholz' claim to the contrary. I was only able to find a horrible (probably machine) translation of the full
statement by Gazprom. Apparently they seem to be saying that shipping the turbine not directly from Canada to Russia was bad (breach of contract, maybe?) and likewise not
shipping it on time, so they are asking for some kind of guarantees they won't be affected by sanctions (again?). Found a better translation here. They seem to be saying that they're afraid of being held legally liable for breaching sanctions in Canada or in the UK if they take delivery from Germany, due to the complicated nature of the maintenance contract.