When you make a command "wrongly" the a letter deletes other characters. I am using mods on the video clip, but this happens on vanilla too
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It appears your control key got stuck for a brief moment, and a got pressed twice in 1 frame, resulting in Control+s -> select everything + a -> replace everything with "a".
Please verify that this is not an issue outside of minecraft.
As mentioned below, please ensure that this isn't a problem with your keyboard. In other words, please verify if this problem occurs outside of Minecraft. Please also check if this problem occurs in vanilla Minecraft.
This issue is being temporarily resolved as Awaiting Response. Once the requested information has been delivered, the report will be reopened automatically.
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Also, does MC-127862 describe your issue? Several non-English keyboard layouts are known to have this problem.

Thank you! MC-127862 describes my issue perfectly. Also its not a ctrl key issue, cause it doesn't happen outside of MC