This is actually strange. Maybe when installing/copying Opal to the ‘user library’ folder, the opal.amxd file was somehow overwritten for this rack version. The folder structure should look like this:
Now I tried to download Opal, and clearly there is a separate Opal.amxd and an additional “rack” folder in which there is also opal.amxd.
Maybe downloading and installing Opal again would help? If this doesn’t help, I would advise you to contact @Ess.