Instinct Solar is shutting down

I think I have the same problem. My clock goes with version 17.00 when starting the activity simply off and also no longer on.
After a restart, I can start the activity at some point. When stopping the activity, the clock then goes off again.
Sometimes the clock goes off during an activity even without pressing a button.
I have also reset the clock without success.

It's happening in the same way to my watch as you explained above. I strongly belive it's a bug that Garmin team has to fix this immediately with a new update. 

In the meantime, I contacted my German support and described the problem.
With this error picture, the clock is now replaced. But I also rather believe that it is a software bug.

I wonder if this is why they seemingly paused the v17 rollout

I will report how the replaced clock behaves under version 17.00. However, the exchange may take three weeks.

I have already received my replacement watch. Garmin support was really fast.
After the update to version 17 everything seems to work normally. I'm still testing though.

I have almost the same issue - when im trying to use GPS related functions or Pulse Oximeter the watch just switches off and i have to switch on it manually.
Support advised me to do next thing to fix this bug:
1) connect watch to the computer as mass storage device

2) Delete such folders from GARMIN folder:
     Activities; Courses; GPX; NewFiles; RemoteSW; Summary; Workots 
3) Delete all .BAK and .TMP files
4) Sync with Garmin Express and update to the latest FW

Test the watch for 48 hours for further bugs

I got this weird notification (y'all got any trash?) last night though. There’s nothing about it on my phone. It’s kind of a hilarious mystery to me but a mystery nonetheless. Any ideas?

What notification exactly? There can be plenty of notifications or alerts not originating on the phone at all.

I have same issue. It started few days ago on walking activity, it turned out that watch shut down at every 1km point when alert sounded. Then I noticed it on running activity, also on lap alert. Then I noticed also PulseOX makes it shut. I don't know if it's related to battery, because it didn't shut when battery is over 53%. I've did @AstroNick suggestion and checking.

Edit: So when battery got below 53% I tried measure PulseOx and first try and watch shuts down, so no improvement...