Matomo + Piwik Pro in parallel - Cookie Problem

I followed the steps in to setup PiwikPro in parallel with Matomo (Method 1).

Both, PiwikPro and Matomo are configured to not set visitor cookies.

I am getting

Error message: Cookie cookie ID (_id) parameter has incorrect length (value: ‘’, correct length: 16)

In the tracker debugger for most of the entries.

Can anyone make sense of this error message?

Page is

Could you please send me a screenshot of the the error message that you are getting?
You can either leave it under this thread or dm me if you prefer to.

currently I cannot find any such occurrences any more in the tag debugger …

No worries, let me know if the issue reemerges.