Your containment procedures are a little short, but honestly that's about all I could see this guy needing.
hitherto undiscovered substance with properties similar to rubber
just take out the "hitherto undiscovered", it's a goofy thing that a lot of people on the site don't like. we can assume this guy's rubber-stuff is anomalous, we don't need to know it's undiscovered.
SCP-4092 locomotes in a variety of ways, most of which appear to be poorly coordinated.
this sentence could be trimmed down - we really just need to know that he's got bad coordination. people locomote in a variety of ways.
ways that do not seem possible within the constraints of conventional physics
this could probably just be "ways that seem physically impossible", it also means you're not using "conventional" two sentences in a row.
"stuck".
kill the scare quotes
SCP-4092 appears to be sapient and is capable of at least somewhat coherent speech.
"is sapient and capable of speech" (you talk about how he's incoherent right after this)
to state that her four-year-old son, Jonathan, was missing.
maybe "to report the disappearance of her four-year-old son, Jonathan"? "state" is such a bland word
Details given to the 911 dispatcher stated
this sentence structure is weird - I would take out the first clause entirely, just say that Mrs. W told the dispatcher [facts].
Mrs. W████████, who had never been divorced or widowed, immediately became suspicious, and assumed that Jonathan had been kidnapped upon not finding him home.
i mean if she's still married to the kid's dad she would probably assume he got kidnapped right away (also say that she's still married to the kid's dad, "never divorced or widowed" is a weird phrasing)
Mrs. W████████, having never seen the alleged “stepdad”, was unable to give further details.
I assume the teacher would've been able to give some details? this sentence could probably just go.
over 144 kilometers per hour
someone converted 90mph to kilometers. round that bad boy up to 150 or down to 140.
posing as FBI.
he's not posing as the Whole FBI. "an FBI agent".
bobble around
"bobble" isn't super clinical but i can;t think of a good replacement so you could leave this one in
the self-inflicted face slamming.
I would just take this bit out, or put that he's uninjured up where he slams his face into the table
involved in its regular pattern of manically stumbling around its cell and slamming into walls,
"involved in its pattern" is a weird structure - maybe "engaging in its usual behavior" ?
removing a pistol from under his pillow
this is irresponsible, and super an action movie cliche. just have it in his nightstand drawer or something.
Researcher ███████ also requested the Foundation grant him a larger firearm for personal use. Request was denied.
also this is super lolfoundation and wouldn't go in the containment documents regardless, i would take that out also
also i think you're a little heavy-handed on the redactions - you could definitely uncensor dates and some of the names.