I had old model Forza 300 2016 before and used it on that one, now I'm putting it on Forza 350 - these have 5 shoes instead of previous 3, Honda has tried to improve this issue, but unfortunately it didn't work...!
You're right about the effect of groves. On my old Forza I also changed to Carbon shoes (they also have Copper). It worked for 25,000 km without issue. But one day I did a full throttle at green traffic light, and one of the shoes broke, the clutch was grabbing, and the bike would stall when stopped. But I could still ride it, only problem was when full stop...!
I manage to get to a Honda dealer, they opened it and changed the shoes to their own OEM, this worked perfectly again for about 10,000 km or so until I sold the bike. When they opened I noticed the groves were still on the bell, almost intact...!
So I realised the OEM shoes work with this aftermarket bell, no need to change. Hence I'm only changing the bell this time.
And before I do all this I had opened, cleaned, cleared dust, sandpapered the shoes and so on, but to no avail.
This time I check more frequently and maybe change the shoes to prevent them breaking like last time, but the aftermarket bell is my only solution that I know works ...
With sintered shoes I'm guessing you mean Copper version they sell..., right.. ? I wonder if that is stronger than Carbon that broke on me...! 🤔 So according to your experience the Copper shoes without aftermarket bell solve this issue as well...? Have you had it over say 10,000 km, because this problem starts around 6000/7000 km on new Honda bikes give or take...
Yamaha owners never reported this until this post. As for Aerox my friend has 96,000 km on his, still same shoes and bell...! No issue... 😎