Sprint 1050 Gt Gear Issues

Hey everyone ! I hope you are doing good.

I'm currently driving a 2011 Sprint 1050 GT.

So, a few month ago, a friend replaced my drive chain, Front and rear sprocket. I saw that to tighten the front sprocket, He put the 1st gear and he used an impact wrench. Since then, I'm having trouble switching from 1st to 2nd, finding neutral is hard when the bike is not moving. I found out that if i'm clutchless shifting I don't have issue to switch from 1st to 2nd gear. I also noticed that if the bike is turned off i don't have any issues (shifting or finding neutral). Went to a mechanic who checked the clutch discs and they are fine. He couldn't figure out the issue tho. Do you guys have any ideas on what it could be ? I know it's hard to diagnose from a distance but im running out of options.

Have a nice day !