Port forwarding not working on NH20A

I'm not entirely sure which step was crucial, so I'll write down my process. I followed the usual steps to set up the router, but it didn't work. I then restored the factory settings, restarted, and reconfigured, but it still didn't work. This was similar to my experience a few years ago when setting up another T3200M.  I called Telus' technical support, and somehow it started working on its own one day. This time, I saw Telus had this online forum to help users, so I came here seeking assistance. However, the issue persisted until two nights ago when I tried accessing the T3200M's WAN IP+port from home, and it worked normally. But when I tried accessing it again from the office the next day, it didn't work. I then realized that I was able to access the T3200M multiple times from home, so I connected my computer to the NH20A and simulated a remote connection to access the T3200M's WAN IP+port, and it worked. After repeating this process several times, I discovered that my computer was connected to a different router's WiFi (i.e., my client computer's WAN IP was different from the T3200M's WAN IP), I could access the T3200M's WAN IP+port. But if my computer was connected to the T3200M, I couldn't access its WAN IP+port.

My NH20A went through the same process.