GS716Tv2 switch. PCs connected via it do not get DHCP IP assigned

Hello, I have recently upgrade/rewire  my whole networking in the office  to CAT-6.

it was a long way comming as the whole wiring was  way too old (at least 20yo most of it and not properly done to begin with. lots of bad drops, dazy-chain 4-8 port hubs mixed from newer 1G hubs to 10yo fast eathernet or even 10K/100K. total disaster). so we had a proffecisnal company come in and layout whole new wiring all over the building.

I have a room (28 PCs) that is wired to the patch-pannel that is fead from 2 switches

one is GS724Tv4 and second is GS716Tv2. all was working for about a week, than all of a sudden, I cam in today to message that 2 PCs can not get onto network. they could not get the IP from DHCP. if I put the static IP all is fine, buit DHCP is lost.  after looking over all of the network and DHCP server I trace it to the GS716T switch. all affected PC where connected through this switch. it is a 2+ yo switch which I decided to reuse after upgrade as it was working fine untill than. since I only have 6 PC connected to it at the moment all other 23 are on the new GS724Tv4

I replace it with an GS108 8 port hub for now. but want to see if I can revise the switch or need to get a new one.

the FW version is(5.4.2.16)  I am getting the .19 version right now and will update. but is it worth it?

PS>> I do not / did not see ANY Errors anywere in logs. the PCs were just not getting an IP when connected via this switch.

 OK a bit of an update here. I have updateded the FW to the latest version of (5.4.2.19) and reset the switch to factory default config. and if I connect a PC to it I can not get an IP address. it's like PC is invisible. it gets the default 169.x.x.x  IP and that is it. again no errors I can see/find anywhere but clients are not seeing the main network.

switch is in an unmanaged mode, no DNS / DHCP services on the switch. all filtering and security is turned off.