I have not found that nitrate changes like that bother my corals. I recall that nitrate does impact alkalinity (I think it lowers it but I forget) so you might want to keep an eye on that. Again, I don’t find your levels or changes concerning on their own. I shoot for >5 ppm, but don’t worry about it much unless it’s near zero. It tends to not get very high in my tanks.
More importantly, in my opinion, is that phosphate may be going up with your heavy feeding. I pay much closer attention to phosphate changes than nitrate. My tanks seem to do well with a wide range of nitrate, but elevated phosphate from heavy feeding tends to result in nuisance algae. Too low of phosphate is an actually a much worse problem. So hopefully you are measuring phosphate too.
