1: Error "load(line): Attempt to index global "F" (a nil value), and "load(line): Attempt to index field "get_express_station_display_lines" (a nil value
The mod itself does not do anything to Advtrains internals - including the "F" table; this looks like an issue with Advtrains itself. Make sure the textline is in the correct LuaATC environment (drop-down in code editor) and that you have a recent version of Advtrains; if this does not solve the problem, please report again and provide more information (what version of Luanti, what version of Advtrains, steps to reproduce, ...).
1: Error "load(line): Attempt to index global "F" (a nil value), and "load(line): Attempt to index field "get_express_station_display_lines" (a nil value
The mod itself does not do anything to Advtrains internals - including the "F" table; this looks like an issue with Advtrains itself. Make sure the textline is in the correct LuaATC environment (drop-down in code editor) and that you have a recent version of Advtrains; if this does not solve the problem, please report again and provide more information (what version of Luanti, what version of Advtrains, steps to reproduce, ...).