Origin of "janky" as in, "This setup is janky."

The term "janky" is common in specific gaming communities and refers to using tactics that are bad or subpar. A specific example from Reddit:

So Reynad just climbed about 800 ranks in legend with this Echo of Medivh Mage deck... Janky as hell but he went 12-1 with it tonight.

A comment explaining the meaning of the term:

"Jank" in [Magic: The Gathering] has come to mean a card or deck which either isn't or doesn't appear to be good. (From "janky", which I think was borrowed from computer science slang.)

The computer science usage is typically something like, "This setup is janky" which is the example I have used in the title of the question. I have personally encountered this usage when referring to computers and various machines that seem to be falling apart or built from subpar pieces.

But where did this word come from?

"Janky" doesn't have an entry in all dictionaries and etymonline doesn't show anything interesting for "janky" or "jank".

Wikitionary also mentions a connection to computer science slang:

(jargon, computing, rare) Unresponsive (of a software application’s user interface), sluggish.

But I am still not seeing anything particularly revealing about this word's etymology.

It's possible it's come from Scottish

OED says of Jank

Jank, v.Sc. (dʒæŋk)
[Derivation obscure: cf. Sw. and Norw. dial. janka to totter, go slowly, hesitate.]
intr. To trifle, shuffle.
1697 Cleland Poems 19 (Jam.) Now he's rewarded for such pranks, When he would pass, it's told he janks. 1808–18 Jamieson, Jank, to trifle. Loth.

So jank n., a shuffle.
1705 Observator No. 4. 22 His pretending to bring Witnesses from the East Indies, seem'd liker a fair Jank than any proper Defence.

But note that the shuffle doesn't mean awkward gait but in this case means An evasive trick, evasion, subterfuge. as detailed in the Dictionary of the Scots Language

†JANK, v., n.

I. v. To trifle (Lth. 1808 Jam.); to desert or jilt; with off, to run off (Ib.); pa.p. jankit, fatigued, jaded (Ib.).
Sc. 1731 Chrons. Atholl & Tullibardine Families II. 380: I wish she be not intised some time hence to make a runaway, and play my boy a slipry trick in janking him.

Hence jankie, adj., not to be depended upon (Kcb.4 1900), and phr.: jank-the-labour, a trifler at work, to trifle at work (Fif. 1825 Jam.).

II. n. A subterfuge, an evasion.
Sc. 1705 Observator (26 April) 22: His pretending to bring witnesses from the East Indies seem'd liker a fair Jank than any proper Defence, seeing it would have delay'd their Tryal some Years.

These are all pretty old citations but do support your descriptions of janky in all the definitions you describe.

OED's Jank: (cf. janka) totter, go slowly and DSL's jank-the-labour: trifle at work for your sluggish computer interfaces.
DSL's Jank (II): subterfuge for your dubious dealing of cards.
DSL's Jankie: not to be depended on for your bad or subpar tactics.

Either someone has a very good memory and quite a sphere of influence to turn an obsolete Scottish word into an internet buzzword or ... sheer coincidence has coined a new word that sounds the same as an old word, is spelled the same (close enough) as an old word and means the same as an old word too.

Modern uses suggesting a Scottish origin are not easy to find but here is one vague claim

https://www.flickr.com/photos/iamthebestartist/5240966543/
2011 Jessamyn West The birds love my janky home made feeder
[After being asked about "janky"]
I assume I got it from my dad's side of the family where they have some scottish-origin words like "banjaxed" and other words that sound sort of similar to that, to me.... Amusingly urban dictionary knows it, so maybe I got it from the internet.

Other definitions

The Concise New Partridge Dictionary of Slang and Unconventional English (2008) has jank, jankity and janky as recent US slang.

jank verb to steal US 2001
jankity adjective old, broken down US 2004
janky adjective broken, dysfunctional, inoperative US 2004

But in the 1984 version of A Dictionary of Slang and Unconventional English: Colloquialisms and Catch Phrases, Fossilised Jokes and Puns, General Nicknames, Vulgarisms and Such Americanisms as Have Been Naturalised he has jank and janky described as

jank, janky. Impudence; impudent: Oundle: since mid-1920s. (Marples.) Perhaps jank is a back-formation ex janky, and janky may be a perversion of jaunty.

In The Official Dictionary of Unofficial English (A Crunk Omnibus for Thrillionaires and Bampots of the Ecozoic Age) by Grant Barrett (2006) there is a 1993 citation.

janky adj. inferior, bad, weird. Also jinky, jainky, jankie, jankey.
Slang. United States. The connection between janky and jinky is uncertain, but as their usage seems interchangeable, I am defining them as a single term.
1993 Usenet: soc.culture.iranian (Apr. 19) “Leave My Login Alone!” You understand what I am saying? Stupid and your shers are very janky, just like you.

It would be handy to know what a sher is to put that into some context but sher seems just as uncommon a word.

The folowing source suggests that no clear etymology is available, but a novel creation might be at its origin.

Janky:

adjective; other word formation type:

• having the qualities of or being associated with a poor urban area or ghetto.

Janky:

• This term has been deemed a more politically correct term for European-Americans (Caucasians) to use than the adjective sense of ‘ghetto.’ It is uncertain what type of word formation process led to the introduction of this word into our language. It is likely to be a novel creation because European-Americans sought to create a more ‘politically correct’ and less racially-charged term for ‘ghetto (adj.).’ It is possible, but probably less likely, that it comes from a variation on ‘junky’ and that the vowel was changed to distinguish it from ‘junky.’
• Etymology : Its etymology has not yet been documented and may remain uncertain, as it appears to have no clear origin or word formation process; however, it was possibly formed as a novel creation by communities of European-Americans. The ‘-y’ suffix on ‘janky’ is an adjective forming suffix; the origin and meaning of ‘jank,’ however, is uncertain and it is not known to appear on its own as a noun. Source : ‘Her car is so janky; I was embarrassed to be seen in it.’ (Conversation with friend, October 2008)

(neologisms.rice.edu)