This is so strange...
Your printer moves repeatedly to X0, Y0, Z250 when instructed by G28,
but it refuses to move when the move is started by G1, but updates Z.
What are the differences between a G28 and a G1 move?
Perhaps it has something to do with the feedrate?
G28 homes with a feedrate set in Configuration.h
G1 uses a feedrate setting that can be changed...
Perhaps something overwrites the default feedrate used by G1?
You can try to specify a feedrate for the move: G1 Z200 F4000
Your printer moves repeatedly to X0, Y0, Z250 when instructed by G28,
but it refuses to move when the move is started by G1, but updates Z.
What are the differences between a G28 and a G1 move?
Perhaps it has something to do with the feedrate?
G28 homes with a feedrate set in Configuration.h
G1 uses a feedrate setting that can be changed...
Perhaps something overwrites the default feedrate used by G1?
You can try to specify a feedrate for the move: G1 Z200 F4000