What causes system overload on MacBook Air?

Your computer is not only pretty old (2012!) but also very weak (CPU, integrated GPU, RAM). A MacAir this old with this specs is not made for extensive audio and video (!) load. Any computation, any plugin costs cpu. Video needs a lot of RAM and CPU. Also make sure you have as much as possible free space on your hard drive available.

You can try some things but some might introduce latency, which you can compensate by delaying your audio and midi regions. But keep in mind this only works with playback, it doesn't work as soon as your are inputting live audio or midi while playback.

• close all unnecessary apps

• increase the I/O Buffer Size to 1024 (introduces latency!)

• work with low sample rates (not higher than 48khz)

• get rid of any plugin in your project by freezing or bouncing the tracks

• use only one audio file per output channel or one stereo file per two output channels.

• cheap video and audio card can cost more cpu

• any mouse twiggling, any display, any moving object (no matter if video or just a virtual knob on your screen) will cause cpu loads because you have an integrated GPU.

it was very hot in the area the laptop was could that have been the cause?

Yes, temperature is an issue. Since your MacAir doesn't have fans, the cpu might be automatically reduced by the system to avoid physical damage of the computer.

You can always check the momentary cpu load of your mac:

Applications > Utilities > Activity Monitor

Besides all the excellent suggestions made, there was a thread from a few years ago which mentions vibration stopping playback at a gig. If your MacBook is too close to a speaker or sitting on something which vibrates move it or place a pad underneath to minimize vibration. It's also a good idea to play the project at least partway thorough before the actual performance. (Not always possible).

What software are you trying to use?

What data are you trying to transfer?

What is the means of data transfer?

How full is your source and destination drive?

What data transfer medium are you using?

The devil is in the details.

A gig? ???

Writing an effective Apple Support Communities question - Apple Community

A gig is where artists play live to audiences, or where DJs do their thing.