Hi, this sounds like double IP exists, even you don’t believe it. Maybe beside Shelly you have other devices with the same IP. If so, change it. A proper documentation of used addresses is always helpful.
Or the amount of DHCP-clients exceeds your DHCP-server its reserved DHCP-IP address range. In this case extend the range.
If it doesn’t help, reset all three Shellies. Join you WIFI network again and set IP-properties to DHCP. Do it one by one, not simultaneously. Advise your DHCP-server to reserve always the same IP to the corresponding device.
Hope it will help.