I'm seeing intermittent issues on some reboots with USB-C-to-DisplayPort adapters: sometimes one of three connected displays gets no input - reboot fixes it. One HDMI-connected LG 65" seems to be reliable. Two 32" Samsungs are connected via USB-C to DisplayPort StarTech adapters. It seems consistent which display it is, might always be the "third screen" on these. I actually have two 2018 Mac Mini i7's set up with the same setup, and sometimes one or both has an issue with one of the 32" Samsungs.... As far as I know, there is no problem with DisplayPort, only with HDMI or Thunderbolt display connections.
A different 2018 Mac Mini i7 with a single HDMI-connected LG 65" sometimes gets no signal to the screen - reboot also fixes.
(It's possible that unplugging and plugging back in would also fix, but these are installed into exhibit structures, so only remote reboot is used for fast fixes for issues like this.)
Once the screen/screens are working, it runs all day without any issues.