I'm guessing the initial drop might be to do with this known issue taken from the 15.23 release notes but is not specific to that version:
Known issues
- After making some configuration changes on MX84 appliances, a brief period of packet loss may occur. This will affect all MX84 appliances on all MX firmware versions
Not sure why that would mean you need to reboot the phones but it could be a trigger?
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