Yeah, none of the plugins for 3.1 will work in 3.5. I grabbed this from the Pixologic support site:
NO plugins for version 3.1 or earlier should be installed in 3.5. They are not compatible with the many changes and new features, and could result in instability or undesirable side effects. Some will even prevent ZBrush from launching entirely.
We are currently updating all official plugins for use with version 3.5. A few will not be updated, but this is only because they are no longer needed. (For example, ZMapper.)
We do not have an ETA on any specific plugin. Please don't ask. Our team is working as quickly as possible and will release each one as it is ready.
I tried and it wouldn't load in. What I ended up doing was exporting the highest subd levels out as objs, importing them into 3.1 and decimating. Reconstructing lower subdivision levels also worked, so you can recreate them if you need to.
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NO plugins for version 3.1 or earlier should be installed in 3.5. They are not compatible with the many changes and new features, and could result in instability or undesirable side effects. Some will even prevent ZBrush from launching entirely.
We are currently updating all official plugins for use with version 3.5. A few will not be updated, but this is only because they are no longer needed. (For example, ZMapper.)
We do not have an ETA on any specific plugin. Please don't ask. Our team is working as quickly as possible and will release each one as it is ready.