What conditions will cause nrf_modem_init() to hang?

I am trying to use libmodem in a bare-metal app on a 9151dk, but nrf_modem_init() is hanging (not returning).  What conditions can cause this?  The issue looks a little like the following issue  

 nrf_modem_init() does not return on SDK 2.0.0 or later 

There was no resolution to that post though. 

I am developing outside of the SDK proper, but using NCS 2.7.0-rc2 and MFW 2.0.1.    

Related