My Apple Watch dims when I am jogging. It is hard to brighten. It is so dim I can’t open settings to adjust the brightness. This makes it impossible to monitor pace, heart rate, etc while jogging. This is a new issue. Did not happen for a year

I'm not sure I understand. Let me explain what happens a little more clearly.

1. When I am jogging I use the Running Ap. I have been using this Running Ap for a year without any problems until about 2 weeks ago.
2. When I am jogging, the screen is dark until I press the crown or tap the screen. Then I can see a bright screen with the info display for the Running Ap. It is very easy to read it even in bright sun. That's as it should be.
3. Recently a few times when I have tapped the screen or pushed in the crown, the Running Ap display comes on but it is so dim it is impossible to see anything. This never happened until recently and even now it usually works properly.
4. After the last episode of this (the 3rd time) I decided to shut the watch off completely and restart the watch. I don't know why that should help but since I did that I have not had a repeat episode of a dimmed screen. Possibly the dimmed screen will happen some time again in the future. I will have to wait and see.
5. Nevertheless I am puzzled as to why the screen would come on so dim. The last time this happened I had run for about an hour and the watch functioned normally for almost the entire run which was a little more than 5 miles. It was only with 3 or 4 minutes to go that the screen dimmed when I called it up. Bizarre.

Thanks for following up and checking with me about this issue. It is not a 3rd party Ap. It is the Apple Workout App with the Outdoor Run selected. I am not sure that the App itself is related to the issue. When you are running the end of your hands are in constant motion and tend to be sort of jerky due to the impact of running. I have wondered if the shaking type motion is related to the problem. It happened again today but I was able to get it back on within a few seconds. It took a minute or two the previous times.

I have not set up any 3rd party apps for running. I quite like this app as it gives a lot of interesting data and enables me to check my progress in real time while I am running. It is very useful.

When this happens the problem is that the view is so dim that it is impossible to actually read it. Nevertheless, you can see that the running app image is there. You just can't read it. For example, the last time I had the problem (not today), it occurred just as I was approaching my home and about to finish my run. So I pushed the knob to change the screen from dark to bring up the screen for the visible running app. This was so I could stop the app for the run. It was so dim I couldn't even see the red X to stop the app. Somehow in that case just by luck I was able to swipe to the right to bring up the screen with the red X (although I couldn't actually see it). And I knew from past use about where the red X was located. I pressed where I thought it was and later when I finally did get a visible screen I found I actually had stopped the app. It was by luck though.

The wake on wrist raise and crown up were enabled but I will reboot and see if that helps. It does not do this every time so it may be a while before I know if it solved the problem. Thanks for your reply.

The thing is, the image did come up but it was so faint it was unreadable. I could actually see that something was there but it was extremely faint. I managed to stop my run because I assumed when I swiped it the image changed to the one that allows you to 'pause' or to 'stop' I punched my finger where I thought the 'stop' button was and I guess I hit it right as in a minute or two the bright easy to read image came back and it was in the 'stop' position. From that image, there is another place where you can push a button for 'Done'.

OK, thanks. Perhaps the restart will help. I will wait until it happens again before I call Apple Support but thanks for the suggestion.