I finally got the ModBus working again. I replaced the original wiring with twisted pair, shielded, 18 gauge strand wire and grounded the shield to the VFD ground. However, this alone did not solve the problem. I still had a TIMEDOUT message after the wire change.
After reading through some more posts I noticed some folks had success after swapping the RS485 + and - wires around. I was careful when I originally wired things up to not get things swapped, but I tried it anyway and the ModBus began working.
In trying to figure out what was going on I noticed the VFD manual showed the RS485 + and - ports one way and the label over the ports on the VFD was reversed from the manual. When I wired things up I assumed the label on the VFD was correct (didn’t think I needed to crosscheck the manual). I can’t explain why things worked for several months with the wires swapped, but if you are having ModBus issues crosscheck the manual versus the label on the VFD to see if the wires are going where they are supposed to.
Thanks to Aiph5u for all your suggestions and time! I appreciate the help.