Kubuntu 20.04 -- USB microSD reader won't mount

I have a microSD (8 GB) that I use for transferring gcode files from my computer to my Ender 3 3D printer. Yesterday, I found I couldn't mount this device (via an unpowered USB hub).

The SD card still reads when directly mounted in the micro-SD socket on the Ender 3, and the card and mini-reader combination mounted and read on my partners Mac (a 2015 iMac with current OS), so I presume this isn't failed flash RAM in the microSD or a bad mini-reader; the USB hub lets me correctly mount and read an 8GB SD card in another reader, but that reader (which has slots for both formats of SD) also won't work to mount the microSD in question.

I'm led to the conclusion that there's a software problem on my desktop computer. I've restarted the machine a couple times without change. I found GParted can detect the microSD and appears to correctly report partition and unallocated sizes as well as used/free in the FAT32 partition, but the option to "Mount" is grayed out.

How can I restore the ability to mount this microSD so I can transfer files to and from it again?

System details: AMD FX8350, 16 GB RAM, known good machine USB ports (except USB3 ports on the back don't work, I understand this is a known issue with Ubuntu 20.04), nVidia GTx750 (1 GB), 250 GB SSD primary and 1 TB platter secondary drives.

I'm not at home at present, so can't post diagnostics now, but will be able to do so this evening and over the next few days.

Starting with the simple stuff, dosfsck -f /dev/sdc1. After clearing the "dirty bit" (indicating I might have pulled the card without "safely remove"), it returned a huge list of errors of various kinds, many of which seemed to indicate it was going to turn bits and pieces of one or more files into independent fragments; I declined to write the results and tried GParted instead, with the result that it threw an error during checking the partition and instead completely mangled the fat32 partition.

In the end, still in GParted, I deleted the partition that came from the Creality factory, created a fresh one (that didn't have several megabytes unallocated at either end), and that one works fine.

In other words: the partition was completely hosed, probably due to inadvertently disconnecting the card while still mounted. Fortunately, the Ender 3 documentation files on it were easily downloaded from the Creality site and all the stored gcode files were copies of ones still on my hard disk; the only losses were a couple "bonus" demo gcodes that came on the card and don't seem to be available from Creality.