Hi @psicompany.com, it's been a while.
Thanks for the additional details and for testing this with both the migrated GPT and newly created plugins. Also, thanks @J_A_G for sharing the additional context.
For the migrated GPT, the current migration FAQ confirms that the replacement plugin starts private, and that the original GPT’s sharing settings do not carry over automatically. Existing users also do not automatically get access to the replacement.
Custom GPT retirement and migration FAQ
For sharing, go to Plugins - Personal - 3 dots - Share and select the option to make it visible in your workspace directory. If the Share option is not available there, you can also check Workspace settings - Permissions & roles - Use plugins - Share plugins to make sure the permission is enabled.
Since you mentioned that the Share control was previously disabled, it would be helpful to see whether that permission is now available and whether you can share the plugin from there.
Let me know if that helps.
-Ziad