EDIT: False alarm, Tom Fulp said it was a bug. May delete this post later. Save this on archive .org before it's too late.
WHILE I WAS WRITING THIS, THE ADS ALREADY SEEMED TO HAVE DISAPPEARED. MAYBE IT WAS A BUG OR TESTING A FEATURE.
i just went on newgrounds and there was this weird empty box. it did not take long for me to realize that an ad was supposed to be there (except its empty, because i have an adblocker); i guess the become a supporter banner didn't convince enough people...
tbh, i'm not too mad at ng for adding ads back, they need to get money somehow, as long as they don't go the youtube route (aka make them play before/during videos instead of just being on the side, and punish people for using adblock) or fandom route (ditto, but even more intrusive ads and fortunately without the punishment) and that nsfw ads only stay in the A-rated area of newgrounds because i dont wanna see that stuff, and newgrounds would get sued by an angry parent of a kid who wanted to play fnf or upload a stolen song for geometry dash (although youtube would get away with it because double standards and they have like a million billion dollars, which newgrounds doesn't).
i'll turn off my adblocker for newgrounds or get supporter because this place is cool :)
ShangXian
You are not alone. I experienced this too, I even made a forum thread about it:
https://www.newgrounds.com/bbs/topic/1547681
waiting for replies from mods or Tom himself.