USB memory stick unmounts and vanishes

I bought this device a few days ago, and checked it with utility f3. It is ostensibly a Philips 256 memory stick, internally seen as an Bus 002 Device 034: ID 090c:2000 Silicon Motion, Inc. - Taiwan (formerly Feiya Technology Corp.) It appears genuine. Yesterday, I was in the middle of copying my video library onto it, when it fell over. Now, whenever I insert it, it persists for a few minutes, and then vanishes. This happens both on my desktop and my laptop machines. I extracted a section of my syslog> I suspect a file corrupted the device, but cannot delete anything. I would like to reformat it, but do not know how. What should I try? I am running Linux Mint 19.1. Is there any other information I might seek out?