Attempting to place a blueprint containing belts, underground or normal, on v1.2.9 causes the following crash currently:

  24.674 Error MainLoop.cpp:1435: Exception at tick 246: The mod Underground Indicators Fixed (1.2.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event UndergroundIndicatorsFixed::on_player_cursor_stack_changed (ID 33)
LuaItemStack API call when LuaItemStack was invalid for read.
stack traceback:
    [C]: in function '__index'
    __UndergroundIndicatorsFixed__/control.lua:41: in function 'render_for_player'
    __UndergroundIndicatorsFixed__/control.lua:202: in function <__UndergroundIndicatorsFixed__/control.lua:200>
  44.475 Info AppManager.cpp:342: Deleting active scenario.
  47.691 Quitting: user-quit.
  47.891 Steam API shutdown.
  47.896 Goodbye

Same here: https://imgur.com/a/NwVPro1