This is a bug when using the old perpetual license Lightroom 6 using the latest Mac OS X versions. The only fix is to simply hide the info overlay by hitting the "I" key or updating your Lightroom to a current version.
Its not really a bug. This worked fine in Lr6 when it was released but is no longer compatible with changes made in the Operating System you upgraded to. There are several other known issues with Lr6 and newer OS's you will probably run into.