Just a simple note: Ethyl acetate is classified as a polar solvent with UV cut-off absorbances at 280 & 260 nm. This has to be taken into account while interpreting the results. Also, when aliquotes were taken out, obviously the volume has decreased. Add to it that the assumed complex formation is a chemical change while the project focuses upon physical change "which is dissolution".
The attached Research Gate reference has important information related to your work.
https://www.researchgate.net/post/What_is_the_UV_cut-off
There are several things that you need to keep in mind. First, make sure the temperature is constant. Is your sample well insulated from your stirrer. Check the temperature of the sample. Heat from the stirrer may be increasing the temperature of the sample. Is the temperature in the lab constant? Second, filter your suspension before letting it settle, then check the melting point and the NMR of the solid residue that you have filtered. You were on the right track thinking about forming a complex of some sort, but think about a solvate or polymorph of the original molecule in particular. The solubility of a polymorph or solvate will definitely change with solvent composition. When doing any solubility determination check for polymorphs and solvates using melting points and NMRs. This is particularly true if you are changing the composition of the two compounds (solvents?) in which you are dissolving your compound of interest. Third, do not do multiple measures of the same sample. Evaporation during handling of the sample can occur. If you do want to do multiple measurements with time, set up multiple samples of the same composition of solvents and handle the measurements in exactly the same way. Fourth, one sample is not enough. Do at least 5 samples of each composition. This allows your to delete outliers.
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