Not only Kaivo and Aalto, but almost every CPU hungry softsynth I own has been giving me glitches and dropouts in Ableton even if I set my buffer length to 512/1024.
I couldn't for the life of me understand why a Core i5-6600K at 3.5 GHz would run like absolute dogshit.
Finally got around to disabling the "Multicore/Multiprocessor Support" option in Live and, lo and behold, CPU usage dropped by ~30% and no glitches for Aalto, Kaivo, Reaktor 6, etc. at 64 samples.
If you are using Live and are having the same issues, give it a try.