Kentico 13 Scheduled Tasks Dynamic WebFarm

What do you mean by dynamic web farm?

As in the web farm isn't in "Manual" mode, so it dynamically generates the name

Yes, but are you adding new servers dynamically somehow? Some auto-scaling? Moreover, most of the affected scheduled tasks are meant to be run on admin app - are you adding multiple admin app instances/servers?
If the web farm is in automatic mode and you have e.g. just one admin and one front end app in the list, that is OK. The task will be executed on that one admin and one front end app. The problem can arise when you have e.g. 3 admins in the web farm - in that case you need to ensure that the task is executed on each of them.
If you are using auto-scaling on Azure - the file system is shared for all the scaled-out instances.

Sorry yes its in automatic mode, so one admin and one front end.

My understanding was by default the scheduled task would just run on the admin one.

Also that there are some tasks that need to be set to run on the front end one.

Is this the case? if so how is that achieved?

If you have one admin and one front end, no action needed. Whatever task needs to be executed and process something on the file system, it will be executed on that one admin and that one front end instance. Problem could be if you add more admins or front end apps - then you need to clone given tasks and set the server names. But still, in majority cases those additional instances are not dynamic. So, you can use web.config keys and set fixed web farm server names.
Exception is the Azure auto-scaling which is dynamic and you cannot use config keys to set fixed server names - because the scaled out instances are using the same file system files anyway, they are not copied to new instances.

But the memory clean for example runs the GC so a shared file system won't help there would it?

Also how does it know whether to run the task on the admin or frontend?

The Clean memory task is just for the admin app - it is an old task which has been there since the beginning and it is not anything crucial.

Thank you, one last question how does it know whether to run the task on the admin or frontend?

Most tasks appear to just run on the admin, do any run on both? if so how does it know to run on both?

If the task should be executed on the live site app, it has to be set so. Please, refer to the online documentation on scheduled tasks