I guess this is a sync error, i.e. from the “Failed Items” list in the web UI?
This means that on the mac the file “foo.ext” exists, and on linux both “foo.ext” and “foo.Ext” exist. On mac that’s not poissible, that’s why it complains. If that’s not the case, please explain exactly what files with that name (case-insensitively) exist, also checking parent directories.
Yes, it’s from the failed items list, and yes, you are correct, it turns out the Ubuntu side has both .ext and .Ext versions. It does explain why the MacOS side fails, I guess, but it would seem that the error message could be a little more on point.