Command-line build blocks itself

We are using Unity 5.5.2f1 on Linux as a build agent for Jenkins. Quite often, particularly when it has to build many assets, the build will appear to block itself. It will have spawned two Unity processes. I have to kill both processes for it to unblock, fail the Jenkins build, and allow the next queued build to start. The last thing output to the log is that it is building a texture (it is always on a texture). This is the output from ps -aux | grep Unity at the time it is blocked.

ubuntu 27781 8.2 1.2 1116008 208380 ? Ssl 11:15 0:36 /opt/Unity/Editor/Unity -quit -batchmode -nographics -projectPath /home/ubuntu/jenkins/workspace/Faily Rider - Android - Master -executemethod BuildScript.Perform_FailyRider_AndroidBuild -buildTarget Android
ubuntu 28448 0.0 0.7 1116008 129324 ? S 11:16 0:00 /opt/Unity/Editor/Unity -quit -batchmode -nographics -projectPath /home/ubuntu/jenkins/workspace/Faily Rider - Android - Master -executemethod BuildScript.Perform_FailyRider_AndroidBuild -buildTarget Android

Is there any command-line parameter or similar that will stop it from trying to use multiple Unity processes to build textures?