Amber Jiang 

I'm not sure why this happens, can only hazard a guess.   I put a small sample here:

{
"gameText": {
"RestoresLife": "Restores \n {0} life",
"RightClickToOpen": "\n<right> to open <right>",
"SniperRifle": "Shoots a powerful, high velocity bullet \n<right>",
"QuantumBlaster": "Unleashes devastating \n cosmic energy \n<left> to charge",
"StealthCloak": "Grants invisibility for {0} seconds \n<right> to activate",
"MeteorStrike": "Calls down fiery destruction \n from the heavens \n<double-click>"
}
}

I would have first expected that making the rule "included" would always manage the tag in the way you want.  However it doesn't and I get the same as you.  So I removed the rule completely and the same thing happens.  I believe this is because the JSON filetype handles line breaks automatically, but unfortunately does this be treating it as a hard break, hence you get the line segmented.  There doesn't seem to be a way to address this.

However, if you use the plugin from the AppStore here, https://appstore.rws.com/Plugin/252 , then you get a better solution (I hope):

Here the line break is correctly treated as such and the sentence is still split, but within the same segment which is what you'd expect from a line break.

Thanks Paul.

Another issue is that the <right> following the \n also disappeared in segment 3.

"SniperRifle": "Shoots a powerful, high velocity bullet \n<right>",

...

Amber Jiang 

Amber Jiang said:

"SniperRifle": "Shoots a powerful, high velocity bullet \n<right>",

This disappears because it's not needed.  Do you need to place this somewhere else, and not at the end of the string?

Yes, I need it appear at the end of the string, so that linguists can know about this tag and the tag content, and place it in translation properly.
Please note that it also disappears from segment 2.

For some target languages, we need to move the tag to somewhere else, not the same place as the source.

Amber Jiang 

Perhaps, because I cannot force the behaviour to do something different (which I think is Studio overriding the behaviour), you can use the "All Content" display in the "Display Filter" or the "Advanced Display Filter"?  When you do that you see this:

You'll see that tags that are considered unnecessary are moved outside the translatable area, but are still there.  So if you need them you can easily put them in there by selecting -> Cut -> Paste into the segment:

I know it would mean manually checking each one, but if you do need it then working in the All Content mode would mean you always know if they are there and can decide if it's necessary on a case by base basis.  In this example I'd be surprised if any of them need moving in given they all appear after the line break.