First, you shouldn’t grid on the snares unless the snare happens to be on the “1” when you count 1-2-3-4. Otherwise your beat counter will be totally off and if you rely on sync your phrasing will be off (esp if some of your tracks are gridded right and others not so much).
Second, the issue with the grid being off, 95% of the time the problem is the incorrect BPM value. You need to set the BPM correctly; easiest way to do it is to tap out the beat and then use the metronome and the grid buttons to fine-tune it. In most cases with electronic music the beat is a whole number; depending on the genre you’re playing it’s often very easy to figure out the right BPM. Then when you line up the first beat on the “1” the whole track should be gridded right all the way through.
You will find some tracks - esp with live drummers - that have BPM drift, and on those you’ll never get the grid perfect. There are other tricks around that but if you’re just starting I’d recommend not worrying about those tracks for now. If you’re playing hip hop, house, dubstep, dnb, etc., this will almost never be a problem.
Go on youtube and look up some beatgridding tutorials. I did a couple of them a while back which you can find if you search for “traktor beatgrids revisited.” It was using an old version of traktor but the rules haven’t changed.