Successful deployment made up 61% of the 848 CubeSat launches between 2005 and 2018. So the Fox line has met industry standards (3 of 5 deployed successfully).

The hardware, even if purchased to be space tolerant, is still assembled and ground based testing in a educational or not for profit environment is limited compared to the big commercial companies. It's the reason why Es'hail 2's amateur component was built commercially using AMSAT specifications.

There is also the issue that as secondary payload CubeSats have been developed to not use active means of deployment. Such as hoping their solar cells, and antennas release. Which is suspected to have caused many failures as has been pointed out. 

Even so, SpaceX is seeing a 5% failure rate on their $2.5 million Starlink Satellites and even NASA's $4 billion Hubble had issues. Space can be unforgiving. And due to size and weight constraints of CubeSats, unlike larger commercial satellites, it's nearly impossible to build redundant systems to keep the satellite functional after any system failures. 

The term acceptable failure rate in engineering comes to mind. And expecting perfection out of a CubeSat just isn't going to happen. 

Dimitrios

VA3DSZ