Welcome to the site !!
What i would check is the cable slack (at the lever) when its cold versus when its hot , if its tightened up , then this will make the clutch slip , you want about 1/4" slack at the lever (i prefer that the clutch disengages right before the lever touches my fingers on the grip , so when you squeeze the lever , the clutch is disengaged just about to your fingers so when it just touches your fingers its fully disengaged)
I would say the issue lies in adjustment , if the basket is new and not notched , then the clutch should not hang , if the basket and inner hub are matched parts , then it should not hang , if all the springs are new , it should not bind causing the clutch to not sit flat , so if all that is confirmed to be working (you can confirm this by removing the small clutch cover with the bike lying/tilted to the left side so the oil does not leak out and actuating the clutch while physically looking at it open/close), then it would have to be in the cable adjustment , or it could also be a bent actuating rod causing the clutch to hang open and not fully return , so the adjustment either at the perch or at the actuation lever where the cable attaches to the bracket is most likely off or the actuation rod is bent , its a compromise between the 2 adjustment points to get the clutch to work correctly , its not all about adjusting at the lever , and again , if the rod is even slightly bent it can hang and cause the clutch to drag or slip
You can test the rod straightness by removing it and placing it on something that you know is absolutely flat and rolling it , if it oscillates even slightly then you know its bent , while the cover is off and before you pull the rod , turn the engine over and watch the clutch basket and make sure it does not wobble either , it would mean the shaft got bent in the incident , its unlikely , but it could happen