Not entirely certain, but it sounds like mabi's "Click Lock" to me. It's a notorious bug, that when a player lags while clicking/pressing a key, whether on mouse or keyboard, it will lock that click until the player pushes the button again.
This can be completely game breaking, when it locks a function key such as ctrl, as you may find yourself perpetually locked onto a mob or npc, and if you try to press things like S, the game is going to look for a hotkey for Ctrl+S cuz that's what it'll think you're pressing. This problem applies to other keys too, major issues occur for things such as alt, shift, tab, and mouse buttons as well. If you can't figure out what's click locked, you'll need to restart, i don't know if a relog can fix it.
I also notice a similar, if not the same, issue occurs for me when i multi-client and alt-tab between the windows, without going to some unrelated third window first. For some reason alt-tabbing between two mabi windows, just completely breaks my functions, and i've yet to figure out the specific reason why, or how to fix it other than alt-tabbing to something like chrome or discord before going to my other mabi window.
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Discord: Tonkatunk#7079
https://github.com/Tonkatunk/Mabi-Pro-Lazyfae-Mods