I've heard of no good reports on mangrove jacks yeasts. many reports of phenolic off flavors, long lag times (3-5 days) etc. The only suggestion i could make would be to try holding it at a high temp for a little while longer, then dropping to "lager" it for awhile.
Honestly, yeast is yeast, any "lager" yeast that says optimal fermentation temp is 20c i would question.