My thoughts are; every chain that I have had on my bike has had, what I call, "tight spots". What I mean by this is, if you have a centerstand mounted on your bike, roll the bike up on its centerstand, put the transmission in neutral, then slowly rotate the rear wheel, (The motor is NOT running!).
As you rotate the rear wheel, watch and check the tension of your chain as it travels around the sprockets. In doing this, my experience has been, there has always been a "tight spot" in the tension of the chain that is felt at some point during the rotation of the rear wheel. This has happened whether the chain is brand new, or one that has been in service for awhile.
When I first encountered this phenomenon, I thought I had a bent countersprocket shaft, or a bent rear axle. I didn't, and I don't.
So, when I adjust the chain to my motorcycle, I do not use the method described in the owner's manual. I use my method: With the bike turned off, I roll the bike up on its centerstand, put the transmission in neutral, rotate the rear wheel, and adjust the chain for proper tension at the "tightest" spot I find while rotating the rear wheel.
What's the proper tension? I don't have a "number" for you! But, there is a visual "drape" to the chain that looks right, (I have done it this way for several years, I don't pay attention to measurements).
As riders have already mentioned, a chain that is too tight, severely reduces the life of your drive system, (sprockets and chain.). If you don't check for a "tight" spot before adjusting your chain, you could be adjusting at a "loose" spot and the tight spot is then TOO tight.
Give it a try and see what you find.