Well I tried wiggling… but without any luck. I then decided to remove the pi from my project and re-solder the specific i2c pins and power/ground pins (on both pi zero and pico HAT) as indicated here:
https://pinout.xyz/pinout/led_shim
I then tried testing the LED Shim on the pi zero header pins directly… without success.
Next steps for me is to solder some header pins on a brand new pi zero, set it up with a fresh SD card and use that for testing… will let you know how that goes.
Thanks again for your help and support!