This is happening because there are libs being staged from 18.04 that have newer versions included in the gnome-3-34-1804 content snap. LD_LIBRARY_PATH looks for libs bundled in your snap first, giving you the opportunity to override what’s provided in the content snap. The downside to this is if you stage a lib (or more likely a lib that depends on other libs) that conflict with something in the content snap, you could be missing symbols.
Your fix is fine, or you could try removing some of those stage packages which could also help reduce the size of your snap. For example, staging gtk-3-examples will bring in a bunch of deb dependencies that will include libgtk and harfbuzz and I suspect gtk-3-examples isn’t useful in your snap.