T22P Firmware Upgrade

[gadgetwizard]

I'm having issues with upgrading several T22P with current firmware 7.61.x.x to 7.7x.x.x (tried 71,72 & 73) from the web page.
I have a 3cx system and was upgrading phones to version 7.73.0.40. I have logged into the web interface of several phones and was able to upgrade fine, however almost a third won't allow the firmware upgrade. I have to remove the existing phone extension's provisioning info (Mac Address, etc) and then login to the web interface and reset factory, then upgrade firmware, then I can add the phone to an existing extension just fine.
I'm trying to figure why the interface doesn't just upgrade on (out of 45 phones, 20ish). This is taking extra time to have to trouble shoot each phone. I also notice the factory reset doesn't really change everything unless you unplug data cable, with 100 phones this is a long task.
I appreciate any ideas/suggestions.
Thank you