The meaning of 論, when pronunced as lún, has already been listed in the answer by @user-487 in another question. However, none of those meaning seems appropriate in the following famous 朝中措 by 元好問：
時情天意枉論量，樂事苦相忘。……
“通‘倫’，事物的條理、秩序” sounds acceptable, but still makes me feel strange. Is there any reliable sources that clarify the meaning of 論 here?
論量/论量 ㄌㄨㄣˋ ㄌㄧㄤˊ/ lùn liáng
依《漢語大詞典》，有二義：
評論、計較。
唐吳兢《貞觀政要‧論任賢》：“至於論量人物，直道而言。”
金元好問《論詩》詩之三十：“撼樹蚍蜉自覺狂，書生技癢愛論量。”
猶思量。
元袁桷《睡覺東西書燈猶明喜勉元達兼示瑾子》詩：“師友淵源端有緒，老夫推枕起論量。”
此處“枉論量”是指“沒什麼好談論計較的”。枉, 白費 (useless)；論，談論 (to talk about, to argue)；量，較量 (to compete with)。
根據《康熙字典》：論
《玉篇》力困切，《廣韻》《集韻》《韻會》《正韻》盧困切；同崘，去聲，義同。
所以，古時即有去聲。
論量:論議是非。(to discuss, to comment on things / on rightness)
(source) So, the original sentence
時情天意枉論量，樂事苦相忘。
might translate as
It is useless to guess the heaven's intention at that time; it is unfortunate that happy things are forgotten.
Very word to word:
The then-emotion, and heaven's meaning, in vain it is to discuss and measure. Happy things --- it is painful --- to be forgotten.
苦 has also the meaning to the full extent, strongly, and orignal meaning of 枉 is bending (becomes: wrong, misjudge, etc.). 相 is a position-filler to invert syntax, because 樂事 is "being forgotten".
My advice is not to be too serious about ancient poems and lyrics, since they are imposed by extremely strict phonetic restrictions of that tune. There are, frequently, inverted syntax, omitted words, fragment sentence, for the form's sake.
What does it mean? I don't know either. But upon looking at the whole lyrics:
時情天意枉論量，樂事苦相忘。
白酒家家新釀，黃花日日重陽。城高望遠，煙濃草澹，一片秋光。
故國江山如畫，醉來忘卻興亡。
The last sentence is clear: a certain country has fallen / declined.
Then I have checked, out of curiosity, Yuan Haowen's biography, you see several things.
Born at the height of the Jin dynasty (1115–1234), he experienced the social unrest and war at the decline of the dynasty. He fled to Henan with his mother when the Jin regime moved their capital.
Since in ancient literature, the speaker is often the poet, we can probably say, Yuan Haowen is lamenting the demise of the Jin government, inherited by Mongolians.
go to http://sou-yun.com/Query.aspx?type=poem1&id=256008 press論量 It is clear is that site.
