Hello from Russia 
So I have very similar problem on my AMD Ryzen 7 1700 CPU. I have a project in Cubase that uses 5 Spires, 5 Kontakts and 1 Omnisphere and with ASIO Guard OFF it’s not running well on 128 (crackles and dropouts), only with 512 ASIO buffer size works kinda fibe. While in FL Studio the same (carefully replicated by MIDI and presets) project works flawlessly on 128 buffer. Turning ON ASIO Guard makes a huge difference tho, it’s possible to work at 128 with no crackles and dropouts and CPU core’s load is pretty even, but I expected much more better performance from Cubase 9.5 Pro though.
Where should I start? Turning off HT in BIOS? Or writing Fabil a PM? Does this problem apply to Ryzens as well as Intels?