barrals should be a solid block and trinsmit a restone signal when resting signal goes through the block. This is the case (if you put a button on the side of a barrel) it will behave as it is supposed to. Although when you leave the world then go back on or close the application, it behaves as a transparent block and needs to be broken and place again for it to behave normally.
Thank you for your report!
We're actually already tracking this issue at MCPE-46742, so I resolved and linked 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.
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