Unitron Moxi Blu - Bluetooth fails matching

I’ve been trying 2 hearing aids couples one week each one: Phonak Audeo Paradise P70 (battery) for first and then these Unitron Moxi Blu B9 (rechargeable). I’ve been using the same phone and I matched the phonaks with wireless bluetooth the first week with no issues then I erased the phonaks entry in my phone’s BT list and matched the Unitrons but I get this problem: this matching stops after some minutes of conversation though the calling is still active, in other words I can’t hear anything and I must stop the calling and then call again!

AFAIK both Phonak and Unitron brands belong to Sonova and they share similar electronics though Phonak’s Paradise platform is not the Unitron’s Blue platform “homologue”, anyway what happened with Unitrons looks a bit strange to me.

Have you experienced this sort of Wireless Bluetooth issue with Moxi Blu hearing aids or with them Phonak equivalent/homologue HAs (whatever they’re)? What’s your opinion about the cause and how do you think that could be solved?