So I am having the same issue with Mac v.10.14.2 (Mojave ). I have downloaded the Spider V Remote v.2.0 from the downloads page on the Line6 website. I ran the installer and it gave me a green check box on the modal indicating everything installed correctly. When I go to my Applications folder I see a Line6 with a red icon and a line through it. The folder also shows Zero Bytes. When I click on it I get the message (The folder, "Line6" can't be opened because you don't have permission to see it's contents.).
I ran the fix mentioned by StationGrey above by entering my password, unlocking permissions and setting them to Read & Write but to no avail. I also tried Read Only but that didn't work either. I even rebooted the Mac on the off chance that would fix something in the file permissions. What is really odd is that the permissions look to be set to someone named "wheel". I have used Macs for over 20 years and have never seen this type of issue with an installer.
If Line6 is listening this is a pretty big deal. Ideally your installer should be installing the app directly into Applications system folder not a sub folder, unless of course there are other folders associated with it. (i.e. plugins, extensions, etc.). Two the installer should not be locking the permissions on the app folder. I am amazed that this hasn't been fixed and if it been fixed via some type of patch that they haven't re-uploaded a new version of the installer.
The Spider V mkII was announced at NAMM 2019 back in January and Mac Mojave was released in September of 2018. That is plenty of time to work through issues like this.