I started experiencing same Zwift mid-ride freezing issue roughly a week ago, it was running just fine before that. Mine runs on a laptop with Ice Lake i7, Intel Iris Pro graphics and Windows 10.
Updating graphics driver to the latest version, disabling BT and trying to run Zwift without any other background programs didn’t help. At this point I think that the culprit is Zwift’s latest update rather than anything else.
I filed a support ticket, still waiting for the solution from them.