When Akrura was taking Krishna and Balarama to Mathura, he stopped near the Yamuna River to take a bath and chant his daily Gayatri. This incident is described in Srimad Bhagavatam 10.39 chapter. As per a few Vaishnava acharyas, when Akrura took a dip in the Yamuna river, Lord Krishna’s form of Svayam Rupa (Yashoda Nandana form) immediately disappeared and the form of Lord Vāsudeva appeared on the chariot. That was the significance behind showing the opulent four-handed form to Akrura.
This way, Lord Krishna indicated to Akrura that now the form of the Lord that would enter Mathura is not Vrajendra Nandana Krishna but an opulent form of Lord Vāsudeva, who exhibits a Kshatriya mood. That place where Akrura stopped is today famous as Akrura Ghata.Acharyas explain that the Akrura Ghata is a transcendental border separating the Mathura and Vrindavana. Thus, Krishna actually never crossed the border of Vrindavana.

Vāsudeva visited mathura, and slayed chanur & mushtik, along with his brother balram.
Shrikrishna slayed his uncle.

This is symbolic for the expression of superiority of dharma.

Vrajavasis felt intense pangs of separation from Krishna only in the manifest pastimes (prakata lila). In His manifest pastime, Lord Krishna disappeared from the vision of the manifest forms of Vrajavasis and went to Mathura through His Vāsudeva feature, that too only for three months.

Thus, the pain of separation felt by the Vrajavasis was due to the fact that Krishna, in His prakata lila, left the Vrajavasis and apparently went to Mathura. Vrajendra Nandana Krishna only went to the Akrura Ghat and then disappeared. So, what happened to Vrajendra Nandana Krishna, after disappearing from the Akrura Ghat?

Acharyas explain that Vrajendera Nandana Krishna resumed His eternal pastimes in His unmanifest form (aprakata lila), which was unseen by common people. The acharyas explain that the abode of Gokula Vrindavana has two types of pastimes: manifest (prakata lila) and unmanifest (aprakata lila). Manifest pastimes were seen by the people around but unmanifest pastimes, which were taking place in the same place went unseen by the common people, on account of the Lord’s Yoga Maya. This unmanifest pastime is completely non-different from that of Goloka Vrindavana (eternal abode of Lord Krishna). This means that both prakaṭa and aprakaṭa pastimes exist simultaneously in earthly Vrindavana, but in the material world, only the prakaṭa pastimes are visible whereas the aprakaṭa pastimes are invisible.

the three months of separation that Vrajavasis experienced when Krishna apparently went to Mathura in prakata lila. But in their unmanifest forms, they were already associating with Krishna, although they didn't know it. This happens through the great influence of the inconceivable Yoga Maya.