Is there any problem with reusing the shank bone that was used on first night Pesach for the seder plate on second night? Since it represents the qorban pesach, I feel like there is good reason not to reuse it, but don't know if this issue is discussed anywhere.
One may not reuse the Zeroa if it was cooked on Yom Tov since it is forbidden to cook on one day of a festival in order to eat the food on the second day or on a weekday. The Zeroa should be eaten by day since we do not eat roasted meat on the nights of Pesach. However if it was cooked prior to Yom Tov to the best of my knowledge there is no issue using the same Zeroa both nights.
Both [the egg and the zeroa] should be cooked or roasted before the commencement of Yom Tov. If one forgot, or the fourteenth of Nissan fell on Shabbos, one may roast or cook them at night (after Yom Tov has begun) (5). One must, however, eat them on the first day of the festival. Similarly, on the second [Seder] night, one should roast or cook them at night, but one must eat them on the second day of the festival.
The reason for this is that one is not allowed to cook on Yom Tov for the second day of Yom Tov, for Shabbos, or for a week day. Thus, if one did not eat the zeroa on Yom Tov, one would have cooked 'shelo letzorech' (if it was just thrown out and never eaten) or violated hachana (if it was eventually eaten). Note that the quote above says that it must be eaten during the day if prepared on Yom Tov. This implies that as long as it is being set up so that it can be eaten on the next day, that is hachana.
Note also that there are sites such as The Shank Bone which point out that the minhag when the zeroa is made on Erev Yom Tov is to deliberately not to eat it.