Ah, that's how long it takes for the mouse to change to held state. Set the value too low & the engine thinks you are trying to do mouse button held instead of left clicking, which ends up making the engine listen out for mouse button hold release state instead of mouse button up state.
I was wondering if you'd changed that value, but forgot to ask. At least you managed to figure out what the problem was in the end.

Anyway, good luck & have fun with developing your game. Also please feel free to join the VS discord server (if you want) @
https://discord.gg/g5zFejW, as we are a lot more active over there than on the forum.