Same thing happens in Waveform. We also have users reporting the same issue with UVI plugins but they don’t seem to have free trial downloads we can test with, unfortunately.
Windows seems to works OK but the problem occurs on MacOS (Ventura 13.2.1).
I don’t have those plugins, but did you or your users try to validate with pluginval? Maybe this gives additional inpout, since it uses a similar approach to the juce hosting.
Also, IIRC some @ujam people were active on the forum, maybe they can test and chime in…
Pluginval uses the same scanning mechanism so usynth.vst will not open here either (in fact, you get the exact same dialog as in the screenshot above).
I rather don’t assume. But the reason I suggested it was, that you might find additional info in the console, other than “failed to load”.
I tried here:
Starting tests in: pluginval / Scan for plugins located in: /Users/daniel/Library/Audio/Plug-Ins/VST/SomeOldProjectOfMine.vst...
Attempting to load VST: /Users/daniel/Library/Audio/Plug-Ins/VST/SomeOldProjectOfMine.vst
Num plugins found: 0
!!! Test 1 failed: No types found. This usually means the plugin binary is missing or damaged, an incompatible format or that it is an AU that isn't found by macOS so can't be created.
FAILED!! 1 test failed, out of a total of 1
*** FAILED
I agree, it doesn’t tell much additional though, but who could have known…
So I can reproduce the issue with some other JUCE plugins that I built in the past.
But other plugins, e.g. BBC Labs validate fine.
I checked lipo -archs that doesn’t seem to be the issue… both archs are present.