I can't understand my reputation chart for today, is it due to rep-cap or something else?
Only for the highlighted part, I mean blank rep for upvote and 8 rep for an upvote, sounds weird. It even started before i completed 200 rep bar.
That is not a bug, it is correct, I checked your reputation tab, you have
4 answers which are accepted, sums up to 60 + 200 Reputation from edits + upvotes
Why you got +8?
You have scored all the reputation points in the multiples of 10s, BUT you have +4 for Suggested Edits and a -2 for an answer, so that creates a +2 offset
So if your total is 192, and you get an upvote, system will serve you 8 points, i.e 200 - 192 (Accepted answers reputation won't count here)
And the blank ones denotes that other users upvoted you on those answers but because of reputation cap, you didn't got any reputation out of it.