Thanks for posting. Here are my suggestions:
1 - It sounds like the phone assigned to extension 100 may be having some network connectivity issues. I saw in the debug that a call was sent to it, but it never responded. If rebooting the phone fixes it, then it is forcing the phone to reregister. The first thing I would try is plug the phone directly into a switchport on the NetVanta 7100 and see if the problem persists. When it is plugged in make sure that is negotiates properly to 100/full and there are no errors on the interface. If this works, then I would investigate the network infrastructure one leg at a time that ultimately connects the phone back to the NetVanta 7100.
2 - I noticed that extension 500's Find Me Follow Me configuration was using "no-press-to-accept" instead of "press-to-accept" for the external number. When it is configured in this manner if the external number picks up for any reason (cell phone voicemail for example) the call will be seen as delivered. To fix this go to Voice > User Accounts > select extension 500 and click Edit > FMFM tab, and check the box for Accept on the external number under Actions. Make sure to click Apply at the bottom and if it works correctly remember to save your configuration. For more information on FMFM see this video: [video] - Configuring Find Me Follow Me (FMFM) on the NetVanta 7100.