Can't connect two monitors via elgato 3 dock

I've got a MBP 2020 with 4 thunderbolt displays and Intel Iris Plus Graphics + an Elgato 3 Thunderbolt Dock. I can't connect two displays (both Dell U2415) via the dock. I've connected one display via mini display to usb-c cable. This one works. I tried to connect the second one using an hdmi cable with an hdmi to usb-c dongle. This one doesn't work. The system doesn't register that monitor at all, like it's not connected. However, if I connect the monitor directly to the second thunderbolt dock of the computer, it works dine. On a side note - I see that the dock isn't fully functional. There are 2 usb-a ports on the dock, but it looks like I can connect only one device to either of them. Tested this using three different docking stations and multiple monitors (same cables/dongles in all situations though). Any help/advice would be greatly appreciated :).