Why has the total area of polygon been reduced after using the splitting tool in QGIS 3.16.6?

I am using the splitting tool to split an original polygon (survey boundary) into smaller polygons (vegetation types).

When I sum the total area of the shapefile after splitting (all the veg types) it is less than the area of the original polygon by 0.1 ha (100.61ha vs 100.71 ha).

Is this avoidable as it creates issues when reporting on the data. As I have only split the original polygon into component parts I would assume the total would be the same.

P.S. It has made me wonder if it is an artefact of the boundaries resulting from the splitting. i.e. do the boundaries take up ‘space’ resulting in less total area in the survey area.