Ongoing or scheduled refresh, recompose, or rebalance tasks can be paused, resumed from a pause, or canceled at any time using the Horizon Administrator console. When a maintenance task is canceled or paused, any operations currently underway will finish, but no new operations will start. When a paused task is resumed, the maintenance operation will continue.
The resources required to perform Horizon maintenance tasks may impact the performance of the Horizon infrastructure. If Horizon maintenance tasks are causing performance problems for Horizon desktops currently in use, or for other resources that share the infrastructure, simply pause the maintenance task. Resume the maintenance task during a period of reduced infrastructure utilization.
I do not recommend canceling maintenance tasks, as this may leave the desktops in an inconsistent state; if the maintenance operation is causing performance issues, simply pause until a more suitable time to resume can...