This article explains that the new Cubasis 3.2 Multicore-rendering only does its magic on devices
“with more than two high-performance CPU cores”
(Cubasis 3.2 - Multicore-rendering & Latency Settings)
I had experienced the same performance issues on my iPad Air 3. After checking on Apple Wikipedia documentation I learned that the A12 Bionic only has two high-performance CPU cores (2.49 GHz Hexa-core (2x high-performance Vortex + 4x high-efficiency Tempest); only iPads Pro includes four high-performance CPUs.
Anyway, not a big deal: I just turned off the feature and everything went back to normal. I started trying different latency options and I found a combination that also works.