There may be a problem if any waves plug-ins are installed.
Please try the following steps.
(i) Close Studio One
(ii) Open the folder "/Library/Audio/Plug-Ins/VST3" in Finder. (From an open Finder window type <SHIFT><CMD><G> and then copy the path "/Library/Audio/Plug-Ins/VST3" into the box that appears.
(iii) In the newly opened folder you should see the Waves-Shell-VST3 9.3.vst3 plugin. Unsurprisingly it looks like a sea shell.
(iv) Move the Waves-Shell-VST3 9.3.vst3 plugin from its current folder to the desktop (or anywhere else that is convenient and safe, by the way there is also a backup copy in the Apps folder...)
(v) Run Studio One, with the iLok connected to the computer. This time Studio One should open successfully. There is no need to open any Songs, it has only to run until its start page.
(vi) Close Studio One.
(vii) Move the Waves-Shell-VST3 9.3.vst3 plugin from the desktop back to its original folder "/Library/Audio/Plug-Ins/VST3"
(viii) Reopen Studio One. It should still open successfully.
If it fails at any stage simply copy the Waves-Shell-VST3 9.3.vst3 plugin back to its original folder "/Library/Audio/Plug-Ins/VST3".