Since Krishna's death has he ever reincarnated or appeared in his ethereal body in this phenomenal world? Have there been any recorded sightings or visitations. I am not asking about other Vishnu avatars, I am asking specifically about Krishna.
Most likely Not.
Lord Krishna got liberated at the end of his life, though he went through the Brahma-loka, the highest of heavenly planes first. While he was killed by a hunter named Jara, he was already in the state of Yoga.
Coming up, Jara beheld a man dressed in yellow robes, rapt in Yoga and endued with many arms. ... Narayana of fierce energy, the Creator and Destroyer of all, that preceptor of Yoga, filling Heaven with his splendour, reached his own inconceivable region. Krishna then met the deities and (celestial) Rishis and Charanas, O king, and the foremost ones among the Gandharvas and many beautiful Apsaras and Siddhas and Saddhyas. All of them, bending in humility, worshipped him. [source]
In above passage after the bolds, it feels like as of something happened after the liberation as well. IMO this could be due to verse translation ordering.
BG 8.16 - All planes along with BrahM-loka are repetitive, O Arjuna. But reaching "Me", O son of Kunti, the rebirth doesn't happen.
Out of devotion, sometimes certain events are regarded as the 'reincarnation' of Krishna.
Shrinathji is a form of Hindu god Krishna, manifest as a seven-year-old child (Balak). ... Shrinathji is the central presiding deity of the Vaishnava sect known as the Pushti Marg (The way of grace) or the Vallabh Sampradaya or Shuddhadvaita, established by Vallabhacharya. Shrinathji is worshipped mainly by the followers of Bhakti Yoga and the Vaishnava in Gujarat and Rajasthan and Bhatia's and among others.
From the Wikipedia article on Chaitanya Mahaprabhu,
The Gajapati king, Prataprudra Dev, regarded Chaitanya as Krishna's avatar
Gaudiya Vaishnavas consider Chaitanya Mahaprabhu to be Lord Krishna himself, but appearing in covered form (channa avatar).
‘nanda-suta’ bali’ yāṅre bhāgavate gāi
sei kṛṣṇa avatīrṇa caitanya-gosāñi ~CC Ādi 2.9
He [Lord Kṛṣṇa] whom Śrīmad-Bhāgavatam describes as the son of Nanda Mahārāja has descended to earth as Lord Caitanya.
As mentioned in this answer, Shrinathji also considered as an incarnation of Lord Krishna.