I also had a similar issue, you should keep an eye on this issue: https://bugs.mojang.com/browse/MCPE-38707
because the new beta doesn't work with most old beta packs, which is this issue's main concern and according to the description of your issue, it's also the problem you are facing.
You'll have to either update the behavior pack or wait till the issue is resolved, because even mojang's own minecon(behavior) pack does not work in the new beta.
they might have downloaded an older version of the pack and always use that rather than the new version, you can fix this by getting a new uuid in the pack manifest.
Here I have proof
I use ios and it happens to me
this happens to me in 1.2 when I exit a command blocks + interface quickly or sometimes when I exit the chat.
This only happens when you use the block/item right after you switch, if you open an interface it resets and the bug dissapears.
Thanks for looking into the case.