Hi MJ-
Just an update on our investigation into the issue, it looks like a small number of sites experienced this issue because after the update, the SCSS code was not recompiled. A quick easy way to fix this is to activate another theme, and then re-activate Cobalt.
We haven’t been able to recreate the error in any of our tests, so it’s still a bit of a “spooky” issue, but this fix has worked for the other users who reported it. Can you give this a shot and let us know if that resolved it for you too?