I can confirm I’m see the same problem in 10.5
I haven’t been able to narrow it down exactly, but in a brand new fresh project file, everything works.
The problem only seems to be in project files that were created in a previous version of Cubase (and have been resaved in 10.5):
Open Channel Settings > Inserts > Save FX Chain Preset > Give it a name > OK
Open Channel Settings > Inserts > Load FX Chain Preset > Choose previously created preset > OK > (nothing happens)
Loading also fails in a brand new project if the preset was saved in an older project.
I know bugs happen, but it’s really quite frustrating - it’s a big part of my workflow that’s now crippled, again.
Worryingly, without knowing anything about the development process at Steinberg, it does seems to indicate there are no unit tests and no regression testing for this to have been broken twice now.
If I get some more time I may try and narrow it down further.