The writer/s are connecting Jesus's coming in judgement to various OT passages that describe God and Son of Man as coming on the clouds or riding on the clouds. There is no secret meaning. This was an ancient idiom drawn from Baal as rider of the clouds. Yahweh and Son of Man are frequently described that way.
1Rise up, O God, and scatter your enemies.
Let those who hate God run for their lives.
2Blow them away like smoke.
Melt them like wax in a fire.
Let the wicked perish in the presence of God.
3But let the godly rejoice.
Let them be glad in God’s presence.
Let them be filled with joy.
4Sing praises to God and to his name!
Sing loud praises to him who rides the clouds.
His name is the LORD—
rejoice in his presence!
17 The chariots of God are twenty thousand, even thousands of angels:
Deut 33:26 ¶ There is none like God, O righteous people, which rideth upon the heavens for thine help, and on the clouds in his glory.
Isa 19:1 Behold, the Lord is riding on a swift cloud
Psalm 104:3 You use the clouds for your chariot. You move on the wings of the wind
Then by the 2nd century BCE this idiom was attached to a "son of man" character:
I saw in the night visions,
and behold, with the clouds of heaven
there came one like a son of man,
2 Esdras 13:3 And I looked, and behold, this wind made something like the figure of a man come up out of the heart of the sea. And I looked, and behold, that man flew with the clouds of heaven; and wherever he turned his face to look, everything under his gaze trembled,
And then all the peoples of the earth will mourn when they see the Son of Man coming on the clouds of heaven, with power and great glory.
The WT spin that it represents invisibility is more than silly given the sentence itself contradicts it.
In the minds of the WT it's all a ruse, the verse says one thing but means another. Secret knowledge only able to be understood properly by them.