Back when Star Citizen was first announced and became a Kickstarter star, the game was powered by CryEngine, with developer Cloud Imperium Games moving over to Amazon's Lumberyard engine in 2015.
Crytek has recently filed a complaint against CIG, with the company stating they agreed to a below-market rate of their license to use CryEngine in Star Citizen, with Cloud Imperium Games agreeing to prominently display the CryEngine logo in their game. Crytek alleges that the use of their CryEngine branding in Star Citizen was a "critical component" of the agreement between the two companies.
Crytek goes as far as saying Chris Roberts himself "publicly sought to minimize Crytek's contribution to Star Citizen".
The lawsuit goes deeper, as Crytek claims that in the terms of its deal with CIG, the developer had to send Crytek a list of bug fixes and optimizations that it had made to the CryEngine source code. Back in November 2015, Crytek reportedly contacted CIG and were after a "long overdue" list of bug fixes and optimizations CIG made to CryEngine, but the developer did not provide them.