Question after adding HDMI switch, monitor goes off after 15-20 minutes

May 26, 2020
I have a nine year old Sony Bravia monitor, KDL32BX320, with two HDMI ports. I've had an old Roku and a newer Nvidia shield hooked to those ports for at least three years, with no problems.

I've added a Univivi 5->1 HDMI switch to the mix. It's separately powered. It allows me to add two computers to the mix, so now four devices go to the Univivi, which in turn is connected to one of the Bravia's HDMI ports.

It works fine, with this exception: for any of the inputs (shield, roku, computer), the monitor goes off every 15 minutes or so. I've turned off all the power saving functions, but that hasn't helped. Any of these four sources, piped directly to the Bravia, keep the TV on, so it's definitely related to the HDMI switch.

What else can I try? Thanks.