That's good you got the rest in crystalline form, but your last crops better hold separately, do not combine them.
If you have some time, try to recrystallize that last product you get to simplify its identification.
I have serious doubts that it's entirely 2,5-DMNS, as it haven't such great solubility to remain so well in your freezed solution.
There is a big chance that your aldehyde is mixed with something else.
I know that your supplier sent you many good quality products, but there is big difference between common simple and cheap reagents that are mass produced in the industrial facilities, and direct or indirect drug precursors that have negligible legit use, especially if we are talking about black/grey markets.
That's why I noted about preliminary quality check in the first place of this synthesis. Chemists often purify their reagents before syntheses even from well-known big suppliers, so in this environment you can't trust anyone's word.
Such technique as checking the melting point is very simple, especially for low melting materials as this 2,5-DMBA.
If it starts melting at least at 45-46C and fully liquefies within +2-3C range, then there is chance of acceptable purity.
Take some video-instructions of how to make this right. Thin glass capillary tube, stirring, slow heating rate over 40C, etc.
As I see you have already tried TLC, that's even better way to detect any adulterants, but you definitely should improve your skills and preferably get some plates with fluorescent 254nm UV indicator, short-wave UV light source (UV-C, completely invisible), filters to protect your eyes, pure solvents etc. Sorry, I haven't time to teach you this here in written form and explain each step. But you can get some good lessons on youtube, of course.
It's a bit costly, but I assure you, if you get good skills with this analytical method, your chemistry skills and reaction yields will make quantum jump from your current level after some practice with organic reactions controlled by TLC.