I will assume that you used the Servers Name (yes that can work with some routers) from the internal LAN
Port forwarding was probably set to a previous internal IP .
When the painters stopped the connection for a long time, the server got a new IP assignment and the port forward is obsolete (or going to the wrong system that goes
)
1) best to set up your router to reserve a specific IP whenever it sees the server machine attach. If reservation is not possible. assign a
Static IP, Subnet mask, DNS server to that system (reserved is the easy way
)
2)match the port forward to the reservation IP