I'd let you know once I can verify this on my side. This resume on play feature works in my setup so I know it works. Just not sure why it didn't on your side.
Until I get it back, can you try:
- In the webapp, go to the software page, select squeezelite 1.6.4-test. Click on "Save". Did the music start playing immediately?
- play a local file (WAV, FLAC, DSD etc). Then shutdown the computer, and turn it on again. Did that play automatically?