Sadly I have some of those issues as well. and I'm still running 2019 on High Sierra!
I have already installed the latest service pack for VW. and I saw no difference in these issues or the amount of crashes.
Lines disappear from few but are still selectable. lines appear offset from the actual location where they are, so when you try to select them the highlight appears in a different place. Editing symbols makes them disappear until I restart VW. Cropping bitmaps makes the image offset from the clipping path (see image attached). And of course crash after crash after crash...
It seems that there are many issues related to graphics. I wonder if there is where the issues lie.
Running dual graphics cards with 6gb of memory each I would assume no graphics issues but there you go.
It's not all to do with MacOS and Mojave. There has to be something else going on since there are people (relatively) successfully running VW in Mojave like Zoomer mentioned.