According to the Mueller report, the investigation was hampered by several issues; like subjects and documents in question living and being held outside of the US, and active deletion of corroborating materials by people associated with the Trump Campaign as noted below:
Further, the Office learned that some of the individuals we interviewed or whose conduct we investigated — including some associated with the Trump Organization — deleted relevant communications or communicated during the relevant period using applications that feature encryption or that do not provide for long-term retention of data or communication records. In such cases, the Office was not able to corroborate witness statements through comparison to contemporaneous communications or fully question witnesses about statements that appeared inconsistent to other known facts.
Mueller Report Volume 1, page 10.
There is absolutely nothing wrong with using encrypted communications. It is something we wish more people would use. Not because of fear of what our Government may find of us, but more in fear of what companies may do with it. In an age of big-data and targeted advertising, encrypted communications has proven to be a small beacon of light we can use to navigate the murky waters of today’s “connected” world.
However, encryption does not mean that said communication cannot be “unencrypted” by the user, if he/she chose to. In other words, just because you and I may communicate using an encrypted application, does not mean that if requested, you or I could not share with the person requesting, said communication.
This means that people associated with the Trump campaign actively chose to keep their communication encrypted, knowing it would hamper the investigation. Furthermore, communication which was not encrypted was destroyed, either through active deletion of the data, or using short-lived messages.
The former is something most people are familiar with (right-click, delete). The latter, are message options, normally in communication applications which use encryption, which allow you to set a “time to live” for your message. Using this method, you can send a message to a person (encrypted of course), set a “time to live”, have it reach the recipient, and have the recipient read it within the allotted “time to live” before it is automatically deleted.
In both cases, I find it difficult to understand why such actions were not considered obstructions of justice.