Since some spells (such as enlarge/reduce) seem to reduce or increase the amount of mass that is present in game-play with no explanation as to how this happens, some interpret that to mean that conservation of mass is “thrown out the window” in 5e.
However, another view is that the RAW is silent on how those spells work, which leaves it up to the DM to either enforce or discard conservation of mass. The detailed mechanics of enlarge, for example, might be that it draws molecular matter from deep within the earth and/or from the environment or atmosphere, or even from another plane, such that conservation of mass holds true. Or then again, it might not. The spell description doesn’t say.
In a couple of answers about 3.5e (such as this one and this one), it has been softly asserted that conservation of mass is not really respected in D&D, and the topic was touched upon in comments to an answer to a 5e question, but the issue has not been definitively put to rest, that I can see.
Is this indeed ambiguous according to RAW, perhaps intentionally (perhaps the rules authors are avoiding over-managing the campaign settings of various tables)? To put it differently: Is the RAW silent on conservation of mass? Or is there a definitive RAW answer to this somewhere that I have not come across?