Updated to 2.8.4 - keyboard input lag, USB serial issues

Hello! I've been chasing this down for a while when I have time and have hit a dead end.I recently updated to 2.8.4 (for a hardware upgrade - long story) and have had a few issues getting my backed up config up and running again.

The first issue is with the OS in general - it hangs for several seconds at a time when I'm entering text. This can be text in the terminal, in a Geany session, in the login screen, even SSHed into the machine - it's bizarre. Everything else about the OS seems appropriately snappy. Text input, if I let it sit for more than 5 seconds, will lag for several seconds before "catching up" to what I've typed.

The second issue is getting VFDmod to work. I have a YL-620 VFD which was working with VFDmod on my prior version (I think it was 2.8.2). On this one, I have installed VFDmod, created a udev rule to map the USB converter, made sure I'm part of the dialout group, verified my vfdmod .ini file is configured correctly, and am still unable to launch. The error in the window is
Attached is the report file in .txt format. Thank you in advance for any help! I've got a project this is holding up... 

The serial interface was never working, and that was the larger issue. I reinstalled the OS multiple times to no avail.

While it's possible I have failing hardware (this is an old Optiplex machine), the 2.8.4 update was the point at which everything went south.

I'm swapping my Mesa card for a FlexiHal and moving to IOSender on Windows.