I was thinking vaguely about it while working on my own, but I couldn’t come up with anything!
If the PC is also connected via Wi-Fi, the only thing I can think of is that maybe the PC has some special designation in the router settings (you need it sometimes for internet games or something), or maybe the PC’s Wi-Fi adapter is in bad shape or has a bad setting. It’s not impossible, since smartphones are often a newer generation and more powerful when it comes to Wi-Fi.
The easy way to test if this is the cause is to plug the LAN cable from the router directly into the PC, but that’s a pain if you don’t have a cable at home.