In relation to the writings of Epictetus or Seneca, what is some adequate criticism to stoicism? Any writings/papers dealing with that in particular?
One name that comes to mind is that of Sextus Empiricus, whose work postdates that of Epictetus and Cicero. You might find it useful to look into :
EMPIRICUS, Sextus, Outlines of Scepticism (Cambridge Texts in the History of Philosophy), ISBN 10: 0521778093 / ISBN 13: 9780521778091. Published by Cambridge UP, 2005.
While so far as I know Sextus does not refer by name to Epictetus or Seneca, the editor points to the likelihood of their views as targets, or at least (more precisely) to their holding views that Sextus criticises on p. 89 (Seneca) and p. 132 (Epictetus).
But these are only glancing references.
There are many criticism of Stoicism that might be made.
Crucially, it has no properly developed metaphysical scheme. It claims the Unity of All but this is left as an undeveloped theory. As a consequence some Materialists endorse Stoicism, which is as daft as a vegetarian endorsing the eating of dogs. The lack of a developed philosophy leaves adherents free to endorse all sorts of conflicting views.
The problem seems to be a determination by Stoics to reject the perennial philosophy and claim Stoicism as a unique doctrine. Yet it is easy to make the connection to Buddhist ethics and ever so easy to argue for Stoic ethics by reference to Buddhist philosophy.
The most devastating (and closely connected) criticism would be that Stoics do not seek or claim to know what is true. It is a conjectural doctrine. This would be why it cannot be included under the phrase 'perennial philosophy'. Hence it is popular with those who like its ethical approach but don't want to change their beliefs about the world. If you read some of Massimo Pugliucci's writings on Stoicism you will see the problem. Materialists sometimes think that Materialism is a doctrine of Unity and Stoicism, being without a clear metaphysical foundation, allows them to get away with this woeful misunderstanding.
These criticisms are made from the perspective of the Perennial philosophy. There will other criticisms made by sceptical 'rational' scientists and philosophers but usually they will be less telling.