Problem with Jack Audio Connection Kit after upgrading to Ubuntu Studio 19.10

My main desktop PC has a H61M-P31/W8 (MS-7788) (MSI) motherboard, with Intel i5-3330 CPU @ 3.00GHz.

The internal audio card is reported as: Intel Corporation 6 series/C200 Series Chipset Family.

Also, I used this audio card, connected through USB audio cable interface, with a Behringer Xenix 1204USB Audio Mixer (reported as PCM2902 audio digital duplex).

I've used Jack Audio Connection Kit with Ubuntu Studio 18.04.3 and 19.04 with the explained configuration and not major problems. I mean: I got audio from and to the computer.

But, I upgraded the OS to the last 19.10 version and now... I cannot to get audio THROUGH Jack Connection Kit!

All the used connections and apps are exactly the same, but... There is not any audible sound!

Even the fact that the PasysTray (Pulse Audio Volume Control) is showing me that there is audio in the Jack audio channels... I cannot to hear it from my speakers and/or headphones connected to the main amplifier through the Behringer mixer.

I have to close Jack Audio Connection Kit to get some audio.

What's wrong here?