In our plugin host (we use Juce 6.0.7) we use the code below to load vstpresets to VST3 plugins hosted, taken from here
The hosted plugins, like brainworx plugins do not load the presets correctly, the values are wrong compared to the values that the presets have when the brainworx plugins are hosted directly in the DAW.
It shows that the parameters are changing but are not correct.
There are now dedicated methods for reading/writing VST3 preset files:
To use this, create a derived implementation of ExtensionsVisitor and pass it to AudioPluginInstance::getExtensions. The plugin instance will call visitVST3Client on your extensions instance, and you can then call setPreset on the provided VST3Client argument.