Hello! 
My example is using Platform Behavior Character with two animations using the automatic collision mask and only one event:
This is the result:

If I remove the “Automatic collision mask activated” the bug not happens even if I set the “Automatic collision mas activated” back.
I won’t post more screenshots or gifs here, but I did other tests without platform behavior trying to collides the objects and the bug also occurred.
Thanks!
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Getting the same bug, hopefully this gets fixed soon. Granted it doesn’t matter whether I change the animation it happens when the automatic collision mask is on either way.
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Hey there, thanks for taking the time to report this.
I confirm I can reproduce it, I created an issue on Github to track this problem: Changing animation with automatic collision mask makes the collision mask non-effective · Issue #5499 · 4ian/GDevelop · GitHub
We’re investigating and working on a fix
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Thanks, Clement!
Another issue related to the collision mask change in the new update 5.2.167 is that: The last update 5.2.167 disappeared with some options inside the editing of points
I don’t know if it’s more practical to investigate both together…
Thanks, it was indeed related to the same change. This will be fixed as well 
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