Its probably either something with one of your apps, or possibly a rouge device that is overloading the hub with messages. Custom user IP/LAN integrations can be especially heavy on the hub if they are coded poorly or mis-configured.
This is why my list of questions that I posted twice above is asking about your devices.
For logs, first thing to look for would be errors and warnings.
Barring that, the Device and App stats pages can be helpful. Enable all the columns on those pages and post screenshots of both from a PC/Laptop or large screen device (just the top 10-20 that is visible at the top of the page).
You can also use the Hub Info v3 driver to monitor the hub stats / memory [RELEASE] Hub Information Driver v3 or the Watchtower app to chart it on the hub [RELEASE] Watchtower long-term metrics app
