Hi Daryl,
I've almost never encountered this issue.
What could make a difference is the Java version, nowadays Servoy is shipping the product including Java, which means that the Java version that you might have used previously remains unused (unless you alter the settings)
As Sean pointed out, when plugins are installed correctly, you would expect an entry in your log file in case it fails to load.
Another thing to take care of once you're ready to deploy is to add the new mandatory entry point in plugins (since 2022.09 release)
Information on this can be found here:
https://wiki.servoy.com/display/DOCS/Cr ... ntryPointsIn developer plugins without the entry point will run nicely (although a log entry can be found after launching developer), once deployed the application server will be unable to find the plugins without entry point and fail to load.
Hope this helps pinpointing your (future) issue