The Disk Creator worked fine with two different thumb drives and two different iso images before the upgrade a couple of days ago.
In addition, I have tried to use the Startup Disk Creator today (after the upgrade) and it is giving me failure messages, see attached screenshots below. After the upgrade, the Lubuntu Software Center no longer appears in the menu under System Tools.
I just upgraded from Lubuntu 16.04 LTS to Lubuntu 18.04.3 LTS a day or two ago.