Routine maintenance tasks are performed as users access the site but it looks like the traffic to your community is not sufficient to run these tasks on time. This will cause significant damage to your community if not resolved. It is recommended that you set up a cron or a web service so that these tasks can be run even when there isn't any traffic coming to your community.

how can i fix it?

Do you have a cron setup to run tasks every minute?  Is that cron job actually running?

The message there, as mentioned, indicates your tasks are not running efficiently. I would suggest setting these up to run via cron, as mentioned. If you are unsure how to create a cron job, you would need to contact your hosting company on this. You can see how to switch to cron here

https://invisioncommunity.com/4guides/advanced-options/configuration-options/task-methods-r343/