When reading resourcepacks created for versions prior to 20w46a, the health bar texture during freezing damage does not exist in the old version, resulting in the empty position when reading those resourcepacks.

Where is the bug in this report? That's how it works. Packs can't define something that doesn't exist, which is the case for the frozen heart. It didn't exist in pack format 6. I mean, files that existed before, for example: purple shulker box, which in the past looked just like regular shulker box and then Mojang has changed it, what caused the pack format to change. If it wasn't updated, "purple_shulker_box.png" was a texture for minecraft:shulker_box and minecraft:purple_shulker_box, because in the old format the "purple" texture was used for the regular one. Same for frozen hearts that are part of the icons.png file.

Your resource pack is outdated and needs to be updated.