Shift key is no longer magnetic

Hello

Sorry to ask a question that may seem silly, but I have not been able to find an answer elsewhere

When I move a segment on a specific time code, the shift key used to allow me to snap this element precisely on my timeline

But now, it doesn't do that anymore, it's not magnetized, now it only allows me to move an element of a "layer" above or below

Maybe I made a wrong manipulation or keyboard shortcut by mistake

I hope you can help me with such a stupid problem

Thanks