Ok... after some detective work and testing with different version of jssc starting with version 2.9.4, I found out that it has to do with running on an ARM32 architecture. Starting with jssc version 2.9.5, it looks like ARM32 is either not supported or has a bug that prevents it from loading the library. There is some talk about this as related to the older Raspberry Pi's on their "issues" page. The solution is to use version 2.9.4 or older when running on ARM32 platforms.
So it's not a Java 8 issue, as I tested the latest version of jssc (2.10.2) on Ubuntu Intelx64 and ARM64 with Java 8 and Java 11+ and it ran fine.
This means that if you are using jserial on an older ARM32-based embedded computer (like the older Raspberry Pi models) with Java 8 or any other ARM32 JRE platform, jserial v1.40 will not work. You will have to use jSerial v1.32 or below.