Just two ideas:
1.) are you using a VPN on your FP? This might interfere.
2.) Is your APN configured in a way you use IPv4 and IPv6? If yes - could you configure it to only use IPv4? In the past (ok, it was a really different problem, but still maybe worth a try…) there had happened weird problems with dual stack (v4+v6) like e.g. here: Android 10 FP3 WiFi Hotspot: Toyota Corolla can no longer access internet