Why display 2 same ad blocks?

It seems your theme calls the_content filter more than once:
https://adinserter.pro/faq/how-ad-inserter-works#multiple-insertions

Set Filter to 3:
https://adinserter.pro/documentation/additional-block-settings#filter

Successfully resolved the problem, but on the AMP page the ad did not appear.

Remote debugging doesn’t seem to be enabled.

has been activated.

AMP pages use different layout / processing so you would need to use another block with different settings (filter to 4 – needs to be tested).

You can also try to remove filter and set Max insertions to 1. This approach may work for both page types:
https://adinserter.pro/documentation/additional-block-settings#insertion