I'm not sure what's going on here; I'm using the OSM highway layer (available here) and have loaded it into Pro; no matter what I do, I cannot get symbol layer drawing to behave correctly when using a casing-style symbology.
My caps & joins are all set to round, drawing order looks right...but it doesn't behave. Is this a known issue with Pro 3.1, or large feature layers?
Even non-outlined symbology draws incorrectly:
What's weirder is if I switch over to the map view and zoom in quite a bit, it looks fine; as I incrementally zoom out, I start to see issues, at first in the areas that I was not zoomed in on, and then another increment out, even that area goes back to not joining, so to speak.
Note the southern segments starting to overlap:
And now totally broken:
On export, when it works, it looks fine, but it's difficult to make a map when you can't see what it's going to look like.