The HUD gets broken when you change the window size since you're using the draw_gui_end function to handle the HUD. Most mods use draw_set_projection(); and draw_reset_projection(); in a Draw event.
https://github.com/saniblues/Past-Nuclear-Throne-Daily-Seeds/blob/master/Lightwe...
This is how Vagabonds does it and it also factors for multiple resolutions and any changes to the viewport. The code I provided just guts one particular aspect of a character from that mod, so all it does is draw a yellow screen over every player's HUD.
I've yet to sink my teeth into the character yet but I'll give my input when I do! Looking forward to playing it
(Screenshot of the code I'm posting in action)