No tftp response

[cowrea]

Heyo,

I got a Omni PCX OXE R11.0.1.
I got 17 Dect and 19 VoIP Phones.
Since this year i got several issues with my VoIP-Phones.

Three of them shows sometimes "No tftp Response" on their Display.
After i unplug them and wait for like 2min untill i again power them they will work again.

I got a VLAN in wich are both, the pbx and the VoIP-Phones.
Cuz i want to access the PBX there is a routing in this VLAN so it is possible for me to even ping them from my local node.

I changed all wires between the VoIP Phones and the Switch which will lock them into the VoIP VLAN.

Any idea how i could fix this issue?
I think some device is "attacking" the Phones so they will crash.
Does the pbx provide me any log in which i could check this?
Normaly i would check the logs of the switch but i havent found something specal.
Some ports are often flapping but not these three.

Right now they are working so I'm not quiet sure if they are pingable while in "no tftp response".

Btw all of them are PoE powered.

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Cowrea