Let up and Lay off

Let up verb - To come to an end.

Lay off and let up are semantically related In some cases you can use "Lay off" instead a verb "Let up".

Lay off verb - To bring (as an action or operation) to an immediate end.

Let up and lay off are semantically related in stop topic. Sometimes you can use "Let up" instead a verb "Lay off", if it concerns topics such as stop doing.