Discrepancies between GA and Piwik PRO

I still see big differences in the number of visitors, sessions, and Google Ads clicks. Piwik Pro shows 21% less visitors and sessions than GAU and 3,5% less clicks on Google Ads.

Can you help me to understand why?

Hi, i’m curious: have you found a fix on this one?
We also see big differences in terms of Google Ads traffic:
GA-U and Google Ads: 550 clicks
Piwik Pro: 307 clicks

I still have the problem as well. And no answer to it.

Can anyone help on this?