I didn't tested numerous custom maps available in this site with 1.31 version. Only my altered melee map that so far worked without issues. Standardly I'm using 1.29.
I haven't even tested it with Reforged just yet, though, as Shar Dundred mentions in one of his post, Reforged brings a lot of bugs and errors.
Sorry, I can't give you any kind of help. And since you also faced similar issues with almost custom maps (not just Struggles), it's possible that those maps might have issues with JASS or something.
This is also one of the Reforged issue as Shar Dundred explained in one of his post.
The only way to fix that "portrait" issue is by modifying the campaign with World Editor so that it doesn't use the new "custom portrait" data. But that would literally destroy "backwards compatibility" with the older patches, which the author didn't want. Other custom campaigns and maps that made with older patches would affect as well.
In theory, even if Blizzard somehow fixed every issues with Reforged, the other will resurface. Therefore, you should play this campaign on the recommended version, which is pre-Reforged ones.