The CPU usage will spike to 100% for no reason, even when nothing is playing. There are sometimes "Pro Tools ran out of CPU power" messages. This also happens with all plug-ins removed from the plug-ins folder, as well as when there is no session open and the software is simply open.
Greatly increasing the buffer helps some, but this is an unacceptable solution, as it adds latency.
I spoke with Avid Pro Tools support and the agent connected to my system. We were unable to resolve the issue.
This is happening on an incredibly-powerful PC, so I know that the CPU is not running out of power.
Intel i9-7900X (10-core, 20-thread processor)
64GB DDR4-2666 RAM
X299 motherboard (Asrock X299 Taichi)
Asrock Thunderbolt 3 AIC
Pro Tools 12.8.1
Windows 10 Pro (Version 1703 - Build 15063.632)
Thermaltake RGB850W power supply
Thermaltake Water 3.0 Extreme 360mm liquid cooling
EVGA NVIDIA GeForce GTX 1080 SC
Toshiba 7200RPM hard drive
Focusrite Clarett 8pre