Can anyone tell me what is the relationship between Anglicans and EOs, and why is it that some EO claim Anglicans (supposesly) do not have valid orders?
The agreed statements can be found here. https://anglicancommunion.org/relationships/ecumenical-dialogues.aspx I can't speak for EO attitudes to Anglican Orders, save that some recent decisions of Anglican Churches have not pleased them.
There has been a complicated history between the Anglicans and EO, with some EO—at various times—appearing to accept Anglican orders. Since there is no central authority for the Orthodox, what one Church (for example, the Antiochians) may have done with the Anglicans at one time, was never binding on others, such as the Russians. Since the ordination of women, and especially the consecration of female bishops, the Orthodox will never (short of a 180 degree reversal of their theology) recognize Anglican orders. The WO issue has created an insurmountable obstacle in that regard.
I would like to briefly mention the fairly new phenomenon of the predatory nature of ROCOR's Western Rite Vicariate. They are actively recruiting Anglican clergy, particularly from the Continuum, and will ordain all callers. This is something of a 'bait and switch' as the Western Rite is meant to be transitional to bringing these folks into the Eastern Rite.