External Monitor Goes Black Intermittently

I have a 15" MacBook Pro (2018) running Catalina 10.15.7. Using a dongle, I have two external monitors connected via HDMI: a HP 27f (primary) and a Samsung LF27T35 (secondary) both connected via HDMI cables to the dongle.

I run my Macbook in closed clamshell (while connected to power) with the two external monitors running and periodically the HP display blacks out for a few seconds and comes back on. It seems to happen after the system has been asleep and woken up, i.e., I don't really experience it upon a fresh boot.

It's more annoying than anything since the display comes on just after a few seconds. Any thoughts as to why?