Problem with offline map

Two years ago I have created several offline maps from Google source with MOBAC which I use regularly, I'm quite familiar with the process. Today I tried to render a map of Barcelona using the same MOBAC version and the exact same settings but when I start Oruxmaps there's an error message "There's a problem with certain offline maps" and the Barcelona map doesn't show up.

I understand that resetting the maps source usually solves those problems but this time it doesn't. After rebuilding the maps source it still reports "problems" (which is quite annoying because I have already noticed that) but no hint to solve them. Another annoying thing is that the "Reset" button is no longer labeled in version 5, I have to guess it's the icon in the upper right corner of the maps menu. So, what am I doing wrong? Like I said I use the same settings in MOBAC which usually led to flawlessly working offline maps. The MOBAC version is 1.8 because newer ones afaik have less map sources included. Are there any changes in Oruxmaps itself, the map format or whatever that prevent the map from getting loaded?

Help would be highly appreciated. Though I might look for ready-made Barcelona maps online I'd like to have a solution to the problem in case of having to use MOBAC again in the future. Thx in advance.

For the map itself, I have a Barcelona map on my computer which I used in Oruxmaps last summer. If you send me a message with your e-mail, I can put it in an online share folder for you.