Polysemy can complicate translation because the same word may have different meanings depending on the context. Translators must rely on contextual clues, collocations, and cultural background to determine the intended meaning.
That's a very interesting question. I can refer to the legal field, which is one of my areas of expertise. Polysemy can create issues, especially to novice translators. Words such as "construction", "consideration", or "term" assume particular meanings in legal texts. Using collocations to tackle such challenges can be advantageous, but most of all, I would recommend consulting sectoral or ad hoc corpora, which help disambiguate words in contexts. Additionally, monolingual dictionaries (i.e., legal ones) are very helpful tools.
Polysemy could be situated in the realm of linguistic diversity, whereby there is no one-to-one correspondence between polysemic lexical items across languages. In other words, one item could be polysemic in a source language but not in a target language. In this situation, only one of the senses of the item will contextually fit. However, where, in my sense, the translation of polysemy may verge on under-translation, is when two senses in the polysemic item may be active simultaneously in the source language, especially in literary translation.