Okay, upon initial first skim, I have to say the whole 'hidden text' thing is a done thing, at this point. It was unique a few years ago, but the idea of it alone no longer makes a SCP article interesting - so you have to have a good narrative to go alongside it, and don't hope that the unusual formatting is the only thing that carries your SCP article. The whole 'haha The Foundation is stupid and I am still around!' thing is also wearing out its welcome a tad. However, I will approach this is a non-biased way - please bear what I have said in mind for your article.

Keter

How do they know it's Keter if it's missing?

HCML supervisor of SCP-XXXX.

Two things - one, whatever a 'HCML supervisor' is could do with a footnote, as I'm not sure and Google only presented me with one Tale that uses the term (and doesn't explain it, from what I can see), and two, there's someone in charge of nothing? It would be much more believable to say 'Site Manager [name]' or 'Project Head [name]' rather than implying there's one person in charge of effectively nothing.

SCP-XXXX is an entity

Is it? But -

All information regarding SCP-XXXX has been expunged from reality due to an unknown cause.

So. How do The Foundation know it is an entity, rather than a phenomena or object? An entity is defined as -

entity

ˈɛntɪti/Submit

noun

1. a thing with distinct and independent existence.

[…]

synonyms: organization, institution, establishment, body, operation […]

2. existence; being.

So how is it known that it is an entity versus any number of other things?

Kohlerson's to blame. He thinks he can eliminate me. Pathetic.

I kind of feel when I read this sort of thing like the SCP object in question is an edgy teenager, not a thing to be really scared or nervous of. Maybe it's just me, maybe other people do find this an effective way to communicate that a SCP object is to be anxious about, but things like 'Pathetic' just strike me as something a 13 year old would say in a YouTube comment as opposed to something that's meant to be intimidating actually being intimidating. Like I said, maybe it's me, maybe I'm jaded and cynical - that's why I always advise when it comes to matters of opinion (as opposed to factual corrections such as typos) to shop your draft around the IRC chat and PM other staff members.

Maybe I'm just an unbearable cynic who needs to get off the computer more and stop basing their opinions on comment sections ;)

All information regarding SCP-XXXX has been recovered from fragments referenced within other files. It is known that SCP-XXXX is sentient, and that it once had a containment team.

Maybe good to explain its designation as an 'entity' here - sentience alone doesn't guarantee 'entity' status.

I found the note about Researcher Hallward somewhat interesting, and maybe that's a good point to try and get a hook in your article.

Makes you wonder if you're working for the good guys, right?

If I had a quid for every time I had read this, or some similar variation, just on this site - well, I'd have a lot of money is my point. It's been said everywhere, from random SCP objects, to Tales (especially involving GAW and AWCY?) to everything in between. It's a cliche, and has at least one Trope page dedicated to the 'good guys' being 'evil' all along - suffice to say I feel it's overused. It is a line that can only be used if there's enough of a narrative for it to be okay, or maybe said in a sarcastic way. Here, it just feels like 'well, this is something that the SCP object would say to make The Foundation really think'. Not really, since The Foundation knows it is 'cold, but not cruel' - I'm sure everyone who's there has questioned if they're really the good guys already, honestly. And people who don't question it, such as the D-Class and some GoI, probably already believe The Foundation is the 'bad guys'.

A notable portion of information regarding a period of seven (7) days, three (3) hours and fifty-six (56) minutes has been expunged in a manner similar to SCP-XXXX.

We no longer do the 'digits in brackets' thing. Instead, you should write out the numbers between one and nine, then use the digits for 10 and up, unless it's units such as measurements. So in this case - 'a period of seven days, three hours and 56 minutes'.

has been expunged in a manner similar to SCP-XXXX. This period of time, designated SCP-XXXX-1,has been "deleted" in a similar manner to SCP-XXXX.

(In bold) you've said the same thing twice here. And how is it similar?

SCP-XXXX-1 to SCP-XXXX is unknown.It's when I became free.

It may be a formatting choice, but you need a space after the fullstop and before the next word ('…unknown. It's when…')

A "Protocol Kohlerson" has been mentioned several times within the database as a containment protocol for SCP-XXXX.

I think you need to make it clearer what information, and how much, is available for this unknown scip. At the moment, it's a bit all over the place, as well as clarity about how it was deleted, despite a recorded 'similar' deletion of time.

Okay. I have to ask. I get what you're trying to do with the formatting thing, I really do.

But uh. Can The Foundation not highlight text to check for abnormalities? I mean, even if you disregard the fact it's not currently 'invisible' (that's only because it's in a tab, so I'm not complaining about that) there's occasionally fairly big periods in between 'visible' dialogue that would make even the laziest of Foundation personnel curious and/or worried there was some sort of hidden message. E.g. -

We simply do not know what SCP-XXXX is, or even if it exists. In order to fulfil our duty, we must know about this anomaly, but we do not. For some reason, all information about this thing has been deleted. All of it. We know nothing. Humans are the bad guys here. Earth used to be so beautiful. Then you took it for yourselves. You took it from me.

There are a few theories on why we know nothing. Unfortunately, none of them have even come close to explaining it.

I put the 'invisible' text in italics here, but it's even more evident on your draft page due to the formatting. There's a random two and a half lines (give or take) between what the 'visible' text says. It wouldn't take a genius five seconds to highlight that, even if it was just to ensure the message wasn't from some sort of double-agent trying to sneak information out of The Foundation. It doesn't help with the realism, to believe that The Foundation would never think to highlight, or that all The Foundation work on computers with a white background, when a dark background is preferable for some people.

Stop living in the dark. You may seek me in the light.

Out of all the dialogue, I like this line the most, because of the reference to "We die in the dark so you may live in the light". Every other line though, is just either cliche, or too much like an edgy teen trying to get The Foundation to open their minds and stop being 'sheeple'. Like I said, maybe I'm a cynical bastard, and other opinions are a.) important and b.) valid. But I do need to tell you how the bulk of this 'hidden' text comes across to me personally, as an adult reader/reviewer.

You've got a half formed idea here, the whole 'missing SCP object' element has been used before but it doesn't mean it can't be again. It's just currently a bit cliche, and pushes too much at being unrealistic in terms of The Foundation somehow missing all this information.