unable to cycle waveforms in ti snow

[r_Look]

hi guys, something so simple as assigning an lfo to cycle the 'osc1 wave select' has problems on my Snow.
sometimes it will start to cycle waves, but only at extremely low lfo rate, like 0-10(??)..and then it does what sounds like a sort of 'buffer pile-up crash' and the audio collapses and distorts, then back to the weird sin wave-ish hi tone it was on before.. strange.
the VSt asks for 512 & lower buffer settings, but trying all down to 32 even doesn't seem to change. ive refreshed the Snow and updated everything, etc. so i wonder what the issue is,
thanks