I also have this problem on a CSS326-24G-2S+RM with SwOS 2.8
I connected the DHCP server to port1 and checked Trusted, and, for all other ports, unchecked Trusted. My Windows 10 laptop didn't get an IP address from DHCP server with this configuration.
If I check Trusted for the port the laptop is connected to, I do get an IP address immediately.
I think this isn't the intended behavior.
I have to mention that I use VLANs, and the DHCP server is on port1 VLAN 500 tagged, and the Windows 10 client is on port24 VLAN500 untagged. I didn't tested this without VLANs.
Anyone have a solution, or any information about this problem from Mikrotik?