ASUS RT-AX88U Pro and DLNA disconnecting

[Supermatico]

Hello to all

I'm just experiencing a brand new behaviour in my LAN with the Pro as a Master and the non Pro as Node:
Since years I'm streaming PC content on my TVs via DLNA using Universal Media Server without problems, two days ago, without any PC nor LAN settings changes, all TVs disconnecting after 150 seconds even if you're watching either a 400Mb video or 25Gb ones

What make me more crazy is this issue happen also in my parents house, 90 Km so far, with an ASUS RT-AC86U

Now, there are just three things in common between these two LANs:
1. All modem/routers are ASUS brand
2. All TVs are Samsung brand
3. All ASUS modem/routers are with Merlin firmware

• The streaming PCs are both desktop ones, so the energy save options are disabled since years
• My ASUS routers had been rolled back to the original latest ASUS firmware, with no fix
• One TV had been restored via Samsung support remote control (with a factory reset) to the original settings , with no fix

Now, I was trying right now to start a stream on a TV and, in real time, watching the Wireless Log to looking for any info can help me to find a solution and I discovered that at least ten connected devices are NOT listed, TV included
Is that a bug?

Thanks in advance