Yealink phones slowdown when attatched to EXP38 panels

I have 2 X T28p`s connected to 3 X EXP38 each


two T28p with 3 X EXP38 panels connected to each phone

The problem is when these phone are connected to the exp38 panels the phone slows down and hangs after a while .

The howto on upgrading the exp38`s firmware did not work

I also have extra power connected to the panels as well

please help