In WL.91 it works fine. Put the plugins in the slots. The interfaces of some concealed, some not. Save master section preset. Unload plugins. Open a preset. It looks like it was saved. But in WL 9.5 all the hidden interfaces are loaded in expanded form. Very bad. Sorry my english.
thanx for the report.
Do you mean that after loading the preset, the GUIs of all inserted plugins are opened up ?
Could it be the same issue as: https://www.steinberg.net/forums/viewtopic.php?f=244&t=125207