This is probably not as alarming as you think.
The "top 4% this month" is reference to your position in the ranking of users who have gained reputation this month. That's somewhat under 700 users this month (and that 4% range covers almost 30 users).
Also, the majority of users exist and operate well below the thresholds the reputation leagues bother to count; for example the statistics ignore the 56,000+ users who have under 200 reputation. Of the users who gained reputation this month, several have gained less than 200 this month (in fact only about 15 have gained above 200), which means that all 56,000 of those untracked users could have gained 198 reputation and still not be counted in the stats.
Essentially, the working set of leaderboard-eligible users is massively small compared to the set of all users participating on the site.
Further, you don't actually have to be actively logged into the site at all to earn reputation, since people can vote on old questions and answers. Glancing through your recent reputation gains, some of them come from positive votes on questions or answers that are almost a year old.
As to your question about the site momentum... voting recently is actually currently higher than average over the last year. As least in terms of the 7-day average of positive votes over the last 365; we had a big spike around November to December, which is normal, and we're currently on a downswing back to the levels that we're usually at for the middle portion of the year. I don't think there's anything worrying about this at all, it aligns with most expectations for traffic and activity spikes (that is, it gets higher around the holidays when people are on vacation, etc).