Is your website in the same timezone? At what time in your timezone did you request the data? (and which timezone is your website in?)

timezone of website is Europe/Berlin. Piwik and website run on same server.
Request was around 7:45 in the morning.

Was the browser maybe open over night? Meaning, before viewing that page, did you completely reload the page or open it directly?

I just had a similar problem before. I noticed when Piwik thinks it is viewing today then the log will only show >= timeStart but not >=timeStart,<=timeEnd and in my case there were already some visits logged "in the future". My case might be a bit different but related code is here: https://github.com/piwik/piwik/blob/3.0.0-b5/plugins/Live/Model.php#L495 Maybe the timezone is not correctly applied when checking Date::factory($dateString)->toString('Y-m-d') != Date::factory('now', $currentTimezone)->toString(). I have seen code parts where we needed to do instead Date::factory($dateString)->setTimezone($timezone)->toString('Y-m-d') instead of Date::factory($dateString, $timezone)->toString('Y-m-d').

Also I think in the first Date::factory($dateString)->toString('Y-m-d') the timezone is missing.

still there in 3.03b1
same visit is shown on different dates (27.03. and 28.03 (today))

This issue has been mentioned on Matomo forums. There might be relevant details there:

https://forum.matomo.org/t/top-date-widget-seems-to-take-server-time-instead-of-browser-location-time/50366/2