i can see the problem:
for some reason you have this code, which is quite different from a ‘normal’ caption code:
<div class="mceTemp">
<dl class="wp-caption alignnone" style="width: 737px;">
<dt class="wp-caption-dt"><img title="kor" src="https://www.nuked.gr/images/level1/alexpolis-camera.jpg" alt="" width="727" height="545" /></dt>
<h1 class="wp-caption-dd"><span style="color: #ffffff; background-color: #0076fb;"> ΑΛΕΞΑΝΔΡΟΥΠΟΛΗ </span></h1>
also, the caption text is in h1 tags.
(i always interprete the ‘mceTemp’ class as sign that something gone wrong in the post editor.)
you could try and re-write the post/page content (?)
-this is very much the end of what can think of ??