Hello,
I'm sorry you are having issues with your devices, I'm just not sure the issue is on the phone itself.
I do have a question and a few recommendations to try and isolate the problem.
Here is the question:
Are the phones only registering to the freepbx or are they being provisioned?
As far as the recommendations go:
1- Upgrade to firmware 7.5.2b (Necessary to upgrade to the latest firmware) then upgrade to 7.5.7.
Here is a link to the firmware download page for the device.
https://software.cisco.com/download/release.html?mdfid=282724650&catid=280789323&softwareid=282463651&release=7.5.7&relind=AVAILABLE&rellifecycle=&reltype=latest
To perform the upgrade I will recommend to be hardwired to the same switch as the phone, and maybe disable the firewall on the PC, because the firmware upgrade software will try to establish a TFTP connection to the phone and in some cases the firewall could prevent the connection from working
2- After the upgrade check if you see less TFTP request, if you don't...
2- Factory reset one of the phones.
3- Try to only register the phone, do not provision it or configure anything else, just make sure the phone can register to the freepbx and see if the TFTP requests will reduce in quantity.
Please let us know if this is helpful.