The answer here seems to be that they are warranty seals. In other words, it seems that the seals were broken deliberately as part of anti-tampering checks by authorized people rather than by accident or malfeasance.
There's some misunderstandings of anti-tampering seals implicit in the question though. So I'll address those even though they have nothing to do with answering this specific question.
(And if the votes are valid, then what's the purpose of having seals?)
A non-broken anti-tampering seal tells an official that the machine does not need to be checked for tampering. So when sealed, it means something. Unsealed it's as if a seal was never applied.
Are the votes counted by a voting machine with tampered seals considered valid?
Consider what happens if breaking seals invalidates votes. A partisan could simply go to a precinct that is expected to vote in a particular direction and break the seals. That's much easier than actually tampering with the vote but it would invalidate the votes on that machine. Rather than making the machine harder to compromise, this kind of rule would make it easier.
The way to use anti-tampering seals is to not put the machine in service if the seals are broken. Or to pull the machine out of service if the seals are seen to be broken after it is already used. Or to trigger extra checks on the machine to verify the votes on it.
At a guess, they (Stein campaign) are trying to renew their argument for a manual count based on the paper record. Remember that the judge said that they had to "show there was a clear and convincing evidence of fraud or other problems" (quoted from the story not the judge). Perhaps they are trying to argue that this is an example of an "other problem" that would require a hand recount of the affected machines.
All this may be exactly why officials did not apply anti-tampering seals. They don't accomplish a lot, and when broken, don't tell you anything useful.
