Why HEIC is different
HEIC is not a simple image file with a metadata block bolted on. It is a container of numbered items, where one item is the picture, another is the EXIF, and a table elsewhere in the file records where each one begins and how long it is. Tools written for JPEG do not find any of it.
How this cleans it
The EXIF item is located through the container's own index, then overwritten with a valid but empty metadata block, padded to exactly the original length. Because nothing changes size, the index stays correct and the file opens normally. The picture data is never touched.
Converting to JPEG first does not help
Most converters faithfully copy the metadata across, because preserving capture information is what photographers want. You get the same GPS coordinates in a different wrapper. Clean the HEIC itself.