for some reason, you cannot place blocks on activated observers. You can easily see this by making an observer loop, then trying to place blocks on it. They appear for a second, then disappear! It also sometimes works near observers, and it's really annoying when trying to place blocks around an observer loop when it has to be activated for some reasons.
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[Mod] OcelotOnesie
InsecurleySecure
Thank you for your report!
We're tracking this issue in MCPE-114259, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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