Dunno if I got your complaint right, but if it is about FPS dropping to 20, it might be due to Celeron55 increasing the parameter value "viewing_range_nodes_max" in one of the latest commits. If I understand it right, that tends to increase the amount of things Minetest has to draw by default, which would explain the problem. At least in wide open areas, that is.
If I'm correct, you might be able to fix the problem by defining
viewing_range_nodes_max = 160
in your minetest.conf.
But I'm no expert on this. OTOH, it doesn't hurt trying, now does it?