User IDs and Unique visitor amounts differ suddenly hugely

Hello dear Matomo folks!

Our website has normally had quite similar numbers for user IDs and unique visitors. For some reason, the difference is 100%, thus the number of unique visitors is 2-fold compared to user IDs…

Would you know any potential reason behind this? I attached a graph demonstrating the difference.

Thanks a lot in advance!

Best regards,

Does this correspond with a matomo software update? Unfortunately, behaviour of the user-id was changed. Before, User-ID forced a user recognition (less unique visitors), now, Visitor-ID has precedence over the user-id. See User-ID: Unique Visitor is not recognized even with the same User-ID · Issue #15593 · matomo-org/matomo · GitHub for details on upcoming changes / options.

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