They were routing all calls such that the CCP could listen to them. [2]
They lied about calls being End-To-End encrypted. [3]
Zoom was founded by a Chinese national and all of their development is done in China. [4]
[1] https://en.wikipedia.org/wiki/Crypto_AG
[2] https://citizenlab.ca/2020/04/move-fast-roll-your-own-crypto...
[3] https://www.techrepublic.com/article/how-zoom-plans-to-bette...
[4] https://technode.com/2020/04/13/is-zoom-crazy-to-count-on-ch...