To reproduce:
Install Combatify (https://modrinth.com/mod/combatify)
Install Legacy4J
Set hud size to a number over 1

Could you inform the version of Minecraft and the mod loader used? The currently supported versions are very different in code, so there are also different problems.
I would like to say that any change made to the vanilla HUD by another mod is subject to problems, especially if it was not done correctly in my understanding, so I will not leave any issue related to compatibility with this open.