I have several devices connected to a Zero Tier network, including two iOS devices. If I try to ping a device on my internal LAN from either of the iOS devices, things work fine. However, if I change the connectivity of either of my iOS devices to be off my local network (i.e.change from WiFi to LTE), I can no longer ping my other devices. I don’t have this problem going in the other direction. That is, a device connected on my internal network can ping either iOS no matter whether the device is on WiFi or LTE.
I found the same situation in the field. I was at a strip mall this afternoon that had public WiFi. If I tried reaching my Pi at home using WiFi, it worked fine. If I try the same thing using LTE (T-Mobile) I get no connectivity.