No I'm not using "ego" in the vernacular sense of pride. I'm using it to mean our conscious sense of being a separate individual existence.
We will always know who we are
That I understand is the teaching. But that is a gloss on the answer to "who are you". You aren't what you appear to yourself to be. This can be demonstrated, examined, analysed from many approaches ancient and modern, eastern and western. Our selves are social psychological glosses on a complex functioning.
I haven't examined this question of why Eckhart was branded heretical, but from my reading of Bernadette Roberts I think that his statement of realization of the fundamental nature of consciousness as singlular did discomfort the "egos" of the church who hold that God and man are separate which is based on the
ego's need to believe that it is something separate with out examining how transitory and utterly dependent the phenomena of a human organism/self is.
Also I think the church authorities rightly realized that Eckhardt's teachings could undermine their control of believers as it moved authority from social church hierarchy and moved it to the awakened consciousness.
lfen