I created a vector tile package using "Create Vector Tile Package" in ArcGIS Pro using the Tiling Format = Indexed. I have used an index Polygon I created with "Create Vector Tile Index". The vector tile works well and looks good until I zoom in to around 1:800, and I get the following strange behaviour in the roads.

If I use Tiling Format = Flat then I don't get this behaviour but then the vtpk is far too big.
I've also tried creating an index using "Create Tile Cache Tiling Scheme" but still get the same issue.
I'm using ArcGIS Pro 2.5.0-beta.1 and also 2.3.2 and 2.4.2
Has anyone come across this before?
Thanks