Asterisk restart after resetting multiple phones

I have 25 Aastra 6753i phones connected to my system (Xeon E3 1230 V2, 16GB ram, 256GB SSD) -
PBX Firmware: 6.12.65-30
PBX Service Pack:
Asterisk Ver. 11.19.0

When all phones reset at the same time and they all try to Get their config. files (HTTP) Asterisk will continue to run for about 5 minutes and reset. During this time the Freepbx GUI does not respond.

Has anyone else seen this or maybe could point me in the direction of what to look for?