Sublabels not appearing for custom layers

[k-kresek]

Description
In MapBuilder version 1.5, when a custom layer is added in the MapBuilder configuration file and sublabel for this layer is defined, it does not appear on the map when the map is loaded. This issue seems to affect only the custom layers, not the GFW default layers.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'https://www.haynatiora.mg/map/'
2. Look at left data panel and open "Limite Administrative"
3. The data sets here should have sublabels but none appear.

Screenshots

Additional context
Seems to have appeared with the latest MapBuilder update - the bug does not affect previous versions.

[k-kresek]

Task complete