https://arstechnica.com/information-technology/2023/02/lastpass-hackers-infected-employees-home-computer-and-stole-corporate-vault/ posted:

“Alerting and logging was enabled during these events, but did not immediately indicate the anomalous behavior that became clearer in retrospect during the investigation,” LastPass officials wrote. “Specifically, the threat actor was able to leverage valid credentials stolen from a senior DevOps engineer to access a shared cloud-storage environment, which initially made it difficult for investigators to differentiate between threat actor activity and ongoing legitimate activity.”

LastPass learned of the second incident from Amazon's warnings of anomalous behavior when the threat actor tried to use Cloud Identity and Access Management (IAM) roles to perform unauthorized activity.

Further Reading
Plex imposes password reset after hackers steal data for >15 million users
According to a person briefed on a private report from LastPass who spoke on the condition of anonymity, the media software package that was exploited on the employee’s home computer was Plex. Interestingly, Plex reported its own network intrusion on August 24, just 12 days after the second incident commenced.