It is well known that understand is a stative verb. But it can also mean "in the process of understanding". So "I am understanding it" sound ok, which suggests that understand is dynamic as well. Any idea on this?
I do not think Understand is an action verb. understand is not used in the progressive forms according to many standard grammar books
I am understanding is ungrammatical and it is not idiomatic and is rarely used by native speakers. It is correct and idiomatic to say : I am beginning to understand , if you are in the process of understanding.
We usually say I understand , I have understood.
I have been understanding is rarely used by native speakers
Here is a link which shows the usage of Understand