Comparing the solubility of glucaric acid and mucic acid
Wikipedia lists the melting points of the sugar acids as:

Glucaric (or saccharic) acid: $\pu{125-126 ^\circ C}$

mucic (galactaric) acid: $\pu{230 ^\circ C}$.


The very great solubility of all the sugary materials (glucaric acid: $\pu{63 mg/mL}$1, or perhaps $\pu{912 mg/mL}$2) is due to their hydroxyl groups, which are very compatible with $\ce{H2O}$. Mucic acid, even though, it has as many hydroxyls as glucaric, is soluble only to the extent of $\pu{3.3 mg/mL}$, although it was predicted from its structure to dissolve reasonably well ($\pu{63.1 g/L}$3). (Note the differences in units; I used the same numbers and units as in the original reference.)
The likely reason for the great difference in solubility and melting point is the way the mucic acid crystal packs. This has shown up in density and x-ray crystallography4.
Looking at the structures, or playing with molecular models (typically, one molecule at a time - you never have enough atoms to make a half a dozen molecules, nor the time to rotate them all and pack them, nor the straight-line vision to see how well they pack) doesn't give you the same sense of difference that the solubility and melting point give.
Maybe this is not terribly unusual: tartaric acid(s), a simpler diacid, shows similar differences in solubility and melting point just because of the chirality of the halves of the molecule. Melting points: D or L: $\pu{171-174 ^\circ C}$; DL $\pu{206 ^\circ C}$; meso: $\pu{147/ 165 ^{\circ} C}$. Solubilities (T=?): D or L: $\pu{1.33 kg/L}$; DL: $\pu{0.21 kg/L}$; meso: $\pu{1.25 kg/L}$ (Wikipedia).
References

https://www.drugbank.ca/drugs/DB03603
https://pubchem.ncbi.nlm.nih.gov/compound/Glucaric-acid#section=Experimental-Properties
https://hmdb.ca/metabolites/HMDB0000639
The crystal structure of galactaric acid (mucic acid) at −147 °C: An unusually dense, hydrogen-bonded structure by George A.Jeffrey, Richard A.Wood, Carbohydrate Research, Volume 108, Issue 2, 16 October 1982, Pages 205-211, DOI: 10.1016/S0008-6215(00)81790-5