WireGuard is not working

On several Mikrotik routers at my customers' premises, I have had WG access to the internal network set up for some time via WG clients on remote computers of various types (PC, MAC). Until recently, routing to individual internal networks behind Mikrotik routers worked without any problems. Some client stations are configured manually, others via BTH. Now, the WG client connects to Mikrotik, but cannot see the devices in the LAN.

Any solutions?

There is always a solution.

What is the definition of "cannot see the devices"?
Do Wireguard clients have access (firewall) to the LAN?

Also, since it worked "until recently", what changed ? Why ?