With the April 19 2024 update, which introduced 64Bit for TF2, some menus such as loadout, backpack and more will fail to display correctly if the value for "settitlebarvisible" inside Resource/UI/CharInfoPanel.res is set to "0", effectively making them invisible.
By default this value should be set to "1", so this problem shouldn't apply to most HUDs but it might still be present for any HUD that mistakenly set the value to "0" in the past.
Note: after bringing back the value to "1", depending on how the HUD is setup, it might also be needed to adjust the "yoffset" value, under the "Sheet" element, in order to ensure that the navigation bar is at the intended height.