Cubase 10 v Halion

I have a recurring issue: I will have a couple of Halion synths in my track, with automation applied. It sounds great on playback. When I mixdown, the synths can disappear completely. I feel it’s a RAM issue. Any advice?

Machine, a 2017 imac, 3.2 GHz 8-Core Intel Xeon W, 64 GB 2666 MHz DDR4