Well, when both Live USB installers failed on two different PCs, I became suspicious and figured that the installation issue didn't have anything at all to do with the live image itself, nor the PC which was having MX Linux installed on it. To test my theory of the issue having to do with the battery notification symbol instead ... which caused an immediate shut-down due to a non-existent (empty or dead) battery ... I then created another live image. This time I removed the battery notification symbol before commencing with a new image that was created within 24 hours of the previous "failed" image.
Problem solved. The new MX Live image without the battery notification symbol then installed properly on the same two PCs where the installation had failed previously.
So if you're a techie like myself who installs images on Laptops as well as on PCs, then just keep that in mind. If you create the image on a laptop with the battery notification symbol present on the taskbar / bottom panel, then there's a possibility that you won't be able to install that image on a PC. In that case, just remove the battery notification symbol from the panel, followed by creating another image specifically for installations on PCs only.