Yes very strange, all your videos look valid for me.
I analyzed your website a bit deeper and took some tests.

On this page that is missing https://mjmartino.eu/item/284-czy-w-joomla-mozna-zarzadzac-baza-danych-joomla-to-proste-7.html you have:

Code:

<p><div class="video-responsive"><iframe width="600" height="450" frameborder="0" src="https://www.youtube.com/embed/yNgCSVauLTw?wmode=transparent" allowfullscreen></iframe></div></p>

on this page that is found https://mjmartino.eu/component/k2/item/89-samsung-bada-os-20.html you have:

Code:

<!-- JoomlaWorks "AllVideos" Plugin (v4.7.0) starts here --> <div class="avPlayerWrapper avVideo"> <div class="avPlayerContainer"> <div id="AVPlayerID_0_f52ad9729d60c37d8b68c0fa14420338" class="avPlayerBlock"> <iframe src="//www.youtube.com/embed/Kcz65Garcco&amp;NR=1?rel=0&amp;fs=1&amp;wmode=transparent" width="600" height="450" frameborder="0" allowfullscreen title="JoomlaWorks AllVideos Player"></iframe> </div> </div> </div> <!-- JoomlaWorks "AllVideos" Plugin (v4.7.0) ends here -->

but both are valid links to Youtube videos. Indeed testing the code in a sample article both videos are found by the videos crawler. I've no other ideas other than some links not crawled, but if you already used the precaching process all links are analyzed.