FLEXLM licensing is used by some commercial software products which includes but is not limited to Abaqus, Allinea, Ansys, Ansys-em, Comsol, Fluent, IDL and MatLab. This is also known as floating licenses as a licence manager or server holds a number of licenses which can be given out to multiple end users of the software. There are a limited number of license and the number available depends on a licensing agreement made in faculty, not in the ARC services.
When a user starts up the software they take a license also called a token from the server. This means there are less licenses available. If more licenses are requested than there are available then a new session will not be able to pick up a license and start using the software. Instead there will be an error message that says something along the lines of the session not being able to start because there are not enough licenses.
When you submit a job through the scheduler on the ARC systems if your job needs a flexlm license it will be picked up when the job starts to execute. Your job will fail if there are no license available at that time. If you run a large number of jobs at the same time then you will be using a large number of licenses which may mean that not all your jobs may be able to run.
Some scientific software may need more than one license to start a session. This happens when the software requires a license for particular solvers as well as for the core product. Many simulation scripts are automatically produced and these may request solver license that they do not need so you may be able to reduce the number of licenses you need by looking at what licenses your job picks up and comparing that to what solvers it uses.
The lmutil will allow you to investigate license status. This utility is installed with MatLab:
module add matlab lmutil lmstat -a