I've seen this bug for many versions now, and I finally decided that I should at least report it and hope it gets patched.
Entities traveling at higher speeds can sometimes phase through blocks that are smaller than 1mx1m. I have provided a clip showcasing this below. In the clip, you can see that I am hitting an Endermite with a knockback 3 shovel. It manages to phase through the fence.
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run modified server software.
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