In Cubase 10.5, if I use one instance of Spark, it's generally ok and behaves as it should. If I load two or three instances, a few seconds after playing, sounds become intermittently distorted, and some time slipping happens. This gets worse the more the song plays. Stopping and starting doesn't correct this - once one instance has gone out of sync, it stays out of sync until I close and reopen the project. The first instance to be loaded is usually unaffected - it's the subsequent ones that have the problems. I don't have this issue with any other plugins.
I'm on Windows 11, and the PC is pretty beefy (i7-10700K, 32GB DDR4). Cubase and the plugins are running off a gen 4 M.2 SSD. The audio interface is an SSL 2, with the latest driver. Latency is set quite high (1024 samples).
Has anyone encountered this before?