It sounds like you have multiple DHCP servers. Most people add additional WiFi routers (access points) without disabling the DHCP service on the router. This is especially true if the client devices are receiving an address in a different subnet, Like 192.168.0.0 and 192.168.1.0
If you have more than 1 AP, check to see if the DHCP service is turned off.
I believe that Shelly devices do have a DHCP server and web server that runs until you configure it for the real subnet and HA address range.That is how the phone app connects to the Shelly for setup at least mine did.
See if the IP range is in the 192.168.33.X range if so, then it has to be a Shelly device
I had a similar issue just occur on my network.
I had been trying to add my Tuya devices (still WIP) to HA and was unsuccessful. Given the complexity and Tuya cloud steps, I assumed that the issue was caused by me not understanding the process. In the morning my network was completely down - DHCP was inop (HA Addon DHCP Server.
Rebooting and even power cycling HA did not help. I had to move the services back to my router to gain network access back.
This is happening to me as well. I was told by another forum as I was having trouble with one of my pc not able to access my main router and the internet. The suggest to run trace route and home assistant appeared to be acting as a dhcp server.
C:\Users\Duc>tracert 8.8.8.8
Tracing route to 8.8.8.8 over a maximum of 30 hops
1 * <1 ms * HOMEASSISTANT [192.168.1.20]
2 * * * Request timed out.
3 * * * Request timed out.
4 * * * Request timed out.
5 * * * Request timed out.
6 * * * Request timed out.
7 * * * Request timed out.
8 * * * Request timed out.
9 * * * Request timed out.
10 * * * Request timed out.
11 * * * Request timed out.
12 * * * Request timed out.
13 * 3 ms 2 ms dns.google [8.8.8.8]
The trace doesn’t say anything about a dhcp server; it just says your trace starts at 192.168.1.20.
The rest of the replies appear to be blocked f.e. by a firewall, but the trace does reach its end destination 8.8.8.8