I would start with Tools > Packet sniffer. Set it to save to a file and only capture UDP packets. Click Apply, then Start and renew the IP on a client. Wait 10 seconds and stop the packet capture. Copy the file to your computer and open it with Wireshark. In the list of packets, you should see a Discovery, Offer, Request, Ack. Do you see all 4?
The Discovery is your client looking for DHCP Servers on the network. There should only be 1.
The Offer is your mikrotik offering an IP.
The client will then deny or request the IP. If denying, maybe the client detects an IP conflict however RouterOS detects conflicts too and skips bad IPs.
The Mikrotik will then acknowledge that the client accepted the IP.
Also double check the basics:
- IP > Pool, check the "Used IPs". You out of IPs?
- IP > DHCP Server, is the entry red which denotes a misconfig?
DHCP is on the correct interface?
- Enable log topic DHCP and renew a client, anything interesting in the log?
Finally if still no success, set a static IP and ping the Mikrotik. If you can't ping or do an ARP lookup to find the router, then possibly a physical connection issue or your smart switch is blocking the MAC of the mikrotik.