Observers will stay triggered when they are in water. When it happens, the broken observers will no longer detect any updates. Though it doesn't happen every time, it has a very high chance of happening. This creates problems with flying machines in water. The flying machines which works properly in air will not work properly in water.
Thank you for your report!
We're actually already tracking this issue at MCPE-64409, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki