Connected monitor keeps waking up

I just got a new XPS 15 9575, connected to a WD19TB dock.  I have a Dell U2410 display and a 2007WFP display, both connected to the dock via DisplayPort (though the 2007 is via a DP to DVI cable, as it has no DP port).  These, plus the laptop's display, are used in a triple display setup with the desktop spanned.  When the laptop is powered down, or when it's in sleep mode, the monitors power down properly and stay powered down.  But when the laptop is on, but the time has elapsed for the monitors to power down to power save mode, the U2410 (and only the U2410) continuously keeps briefly waking back up, then going back to sleep.  It's only "on" for about one second before powering back down.  The cycle is frequent, but not consistent:  it might stay asleep for 7 seconds, or it might be 25 seconds, but I've not seen it stay powered down much longer than that before the next power up blip.  I previously had both of these monitors connected to my old desktop for years without issue.

Any ideas?