After moving the site to https, I caught glitches, how to win?

Question

Nginx

There is a site, a forum vbulletin
Transferred it to https, more or less debugged, it works
But - the external visitor tracking system (matomo) stopped working
It can be seen that the user is logged in, but his further steps on the site are no longer displayed. I looked briefly on the Internet for a solution - I did not find it right away.
Where to dig?
Let me remind you the site on https - - a counter on http - maybe a plug here?

Answer 1

The problem was solved when the site with visit statistics was transferred to https - everything went the same way.
And third-party counters already have https:// in the code line

Answer 2

Google "Mixed content". Of course, unencrypted connections from an HTTPS site are blocked.