ACS sessions disconnecting

All,

V7R1, using ACS.

About 2-3 weeks ago, on 2 of our Windows 10 desktops, the 5250 sessions
started disconnecting after a relatively short period of non-use. Like
maybe 10-15 minutes. One desktop is local, the other is remote via VPN.
These are the only 2 desktops doing this, all other desktops (Win 7 and Win
10) are fine. For that reason, I'm assuming it's something at the PC
level, hence posting to this list.

You can reconnect with a mouse click.

The night before this started, our Meraki MX60 routers received a firmware
update, but I don't see how that would affect this. But I thought I'd
mention it.

I'm concentrating on the local one right now because it's easier to
troubleshoot local.

I have checked the power settings of the desktops. They never go to sleep.

In ACS, I went to Communication/Configure/Advanced and set Keep-Alive to
yes. No joy.

In ACS, I went to Communication/Configure and set Auto-Reconnect to yes.
No joy. (But the use did notice.)

The local one has had 2 java updates since and still no joy.

What else should I be looking at?

Thanks.