As your snap is using classic confinement, this is probably due to Snapcraft patching an RPATH into your plugin so it preferentially chooses libraries under /snap/core/current/ over those found on the host system. This is usually something you want to make sure your app runs against the expected libraries rather than a mix of host and snap libraries.
If you explicitly want to run an executable that mixes host system and snap libraries together, this could cause a problem if you end up loading a library from a snap that shadows a newer version from the host: if you then try to load some host library that depends on features in the new version of the shadowed library you could get a link error like you’ve seen.
You can turn off Snapcraft’s patching by adding build-attributes: [no-patchelf] to the part that builds the library in question. With this option, it is up to you to set the RPATH if needed on your executables and libraries. I’ll note that you’ll almost always find some system where your classic snap malfunctions if you’re mixing host system and snap libraries together.