Unity version: 2018.4.17
Mapbox SDK version: 2.1.1
It seems that the inspector settings in "MAP LAYER" / "Enable coroutines" are ignored. After checking VectorLayerVisualizer it looks like that _performanceOptions is related to each specific sublayer feature, not to a global setting. If in code I get the sublayer feature and use performanceOptions.isEnabled and performanceOptions.entityPerCoroutine, everything works as expected.
This has been tested in play mode in editor, not with "Enable Preview" in editor.