Related to MC-1607, though may be closed as a duplicate. A second "ghost portal" has begun to appear when an End Portal is created, but this one moves across the horizon rapidly, compared to the stationary one in MC-1607. They both are present depending on the angle of elevation. Of note is this one is far more noticeable in the Overworld.
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Ghost portal from MC-1607 isn't stationary, check out the duplicates of it.