Sluggish performance

It has been 2 months since I purchased meteor 350 and I have driven till now 900km. From last 2 weeks I see below issues:

1. When bike is being used continuously for 30 mins I see sluggish performance. I stay in Bangalore so usually gears stay at 1 or 2 while riding (because of traffic) and in that I feel change in bike performance.

2. Sometimes while changing gear from 2 to 1 it does not go, it bounces back to N. It’s like I feel the miss of feedback which happens when shifting gears (I have to release full pressed clutch little bit, to solve this), is this common?

3. I feel vibration in the foot rest of clutch (I mean where we keep our leg and change gears), is this common?

4. The fuel mileage has been decreased before 1st service I found it more (I know it sound strange) but I am not able to understand what’s the issue. I also have doubt whether service center changed the air filter after 1st service (it was done month back), can I check and verify in my own now?

What should I do?