On https://www.mediawiki.org/wiki/User:Evad37/sandbox/mapframe, example 2a shows a map with geoline data. That data is displayed on the fullscreen dynamic map, but not the thumbnail/static map.

Meanwhile, example 2b shows a map with geoline data from a different item. That data is displayed on both the fullscreen dynamic map and the thumbnail/static map, as expected.

I've got some further examples on that page which have different relation types on OSM, since it seems similar to T156433 -- but this bug with example 2a does not seem to be a duplicate, since it works in one map view but not the other.