T28 packet loss / delay error

[crafty]

Every morning on 14 pcs of T28 phones I have delay.
After 1 year since I started to use T28 phones suddenly last week all 14 pcs from one of my network has developed an strange problem.

The problem:I initiate a call from phone no.1 to phone no.2 and only after 7 seconds I can talk.
During this problem I have a lot of packet loss. The computer connected in phone is working fine (no packet loss).
In the same network, in the same switch I have also T19 phones working very good.
After a daily restart (unplug power cord), in the morning, everything working fine for the rest of the day.

Version
Firmware Version 2.70.0.140
Hardware Version 1.0.0.39
Network
Internet Port Type Static IP
IP Address 192.168.0.162
Subnet Mask 255.255.255.0
MAC Address 00-15-65-47-37-0F
Link Status Connected
Router IP Address 0.0.0.0
Device Type Bridge
Router DHCP Disabled
Register Status Account1 140@192.168.0.35 : Registered

Can you help me please?
Thank you!