Vulcanberry

Thanks for the response - the m.2 slot uses chipset lanes, as does PCIe x16 slot 3. Only PCIe x16 slots 1 and 2 use CPU lanes from what I have been able to work out. I should also add that the problem also happens with just the PCIe extension card plugged in (i.e. without the drive actually installed in it).

The PC: PCPartPicker Part List CPU: Intel Core i7-6700K 4 GHz Quad-Core Processor Motherboard: Asus Z170 PRO GAMING ATX LGA1151 Motherboard Memory: G.Skill Ripjaws V 16 GB (2 x 8 GB) DDR4-2666 CL19 Memory Storage: Samsung 950 PRO 512 GB M.2-2280 NVME Solid State Drive Storage: Samsung 970 Evo Plus 1 TB M.2-2280 NVME Solid State Drive Storage: Seagate Barracuda 3 TB 3.5" 7200RPM Internal Hard Drive Video Card: MSI GeForce GTX 1080 Ti 11 GB DUKE 11G Video Card Optical Drive: LG WH14NS40 Blu-Ray/DVD/CD Writer Wireless Network Adapter: TP-Link Archer T9E PCI