Hi, Kent!
I'm just getting started (2.91) and when I try to save and reacquire my preset, it looks like some of the settings didn't take and the tree looks like it has saved as an earlier iteration. Could it be a 2.91 thing?
Are you leaves disappearing when you load the preset? If so, I ran into this issue in the second lesson of the coures: https://cgcookie.com/lesson/modeling-tree-variations?wtime=33
The "Limit Import" option disables some settings from the preset load to optimize viewport performance. If your preset has a ton of leaves, for example, this option will ignore the leaves so your viewport doesn't slow way down.