I think your best bet would be to try and capture a log or do some monitoring to see which specific tasks are using a lot of resources at that time. That will give you more insight into what’s going on. You could do that with a command like htop - htop.dev
Does it happen on a set interval or is it random? If it’s an interval that seems to have a pattern, you could have a service running that is doing some sort of maintenance task, or has some cron job.