@ochranakorona thanks for reporting!
We’ve been investigating this error, but do not yet know the cause.
Could you try the following troubleshooting steps:
1) Try to connect to Site Kit in an incognito browser window
2) Use the Health Check & Troubleshooting plugin and enable its troubleshooting mode. This mode disables active plugins and switches to a default theme safely since it only affects the experience of the logged-in user.
– Please enable the Site Kit plugin and let me know if the issue is present.
– Enabling plugins and your theme one by one in this mode may help pinpoint if something else is involved.
– Note you can disable troubleshooting mode from the plugins page.