One thing that changed from Cubase 13 to Cubase 14 on Windows, is that Cubase 13 defaulted to allowing VST2 plugins, and Cubase 14 defaults to exclude VST2 plugins.
So my theory currently is:
It’s possible that the different behaviour is caused by the same Cubase project using the VST2 plugin in C13 and using the VST3 plugin in C14. – This may not be obvious unless you specifically look for it.
So if the Bypass handling has to be programmed slightly different in VST2 vs VST3, it’s possible that some plugins have a bug in their VST3 versions, that wasn’t in VST2.
From a variety of impressions with different plugins, I’ve come to suspect that something about Bypass handling has changed from VST2 to VST3 and not all plugin makers have gotten this right in all of their plugins.
p.s. Just now, I was also able to find a thread that seems to imply exactly that: