Problem in the base map.
In the northern part of Greece, your base map shows an "orphan" border line. (marked with the yellow circle)
Obviously, this is wrong.
I checked with OSM and ( of course) no such line exists.
Please correct it.
@Gkikas-LGPZ Hi, thank you for detailed report. I put this bug in our internal issue tracker for maps. We are not able to generate new maps "on-demand", but we will fix this in the next release of the base map along with some other bugs.