UV-Vis Spectra: Multiple peaks for one component
Different functional groups may show different absorptions and even a single functional group may exhibit two signals in your UV-VIS spectrum, e.g. corresponding to $\pi,\pi^*$ or $n,\pi^*$ transitions.

While HPLC grade methanol is typically much cheaper than acetonitrile, it might not be the best choice here. You might want to have a look at the cutoff wavelengths of different solvents.

I'd definitely give measurements at $\lambda = $ 280 nm a try.