Single branch on Itoigawa has browning tips-help

Hello, new member here and thought I’d give this a try and see if i can get some help. My large field grown itoigawa has browning tips on one branch for the last 2 months. I’ve noticed that a few smaller branches are now showing some browning tips as well.
I’m wondering if this is a stress issue as 10 days before the browning started I had did some grinding shari work up the trunk. The trunk had already been shari’d almost a year ago, I just used a grinder in September to widen the area going up and around the trunk following the twist. I also applied lime sulfur to the area 2 days after. Now I know I shouldn’t have done that.
Could this be stress or something else? I already checked for mites and found none, I also sprayed just in case. What is odd is that it started on just 1 branch. Pics added to show this. One pic shows 10 days after i did the grinding work and others are today.
Thank you for your help

Initially I was going to ask if it could have been sunburn.

I am wondering now where the grinder was positioned? Is the area circled in blue where you were working with the grinder?

If that’s the case could you have touched the body of the grinder against the branch? Also how close is the base of that branch to where you used the grinder? Could you have caught the love vein?

Thanks for your reply. It was not sunburn as i kept it under 50% shade cloth. The grinder location is lower down the trunk. Adding more pics to show shari work and you can see the browning branch in right foreground well above the location.