NRF_GZLL_MODE_SUSPEND nRF52 SDK 15

I would like to use Gazell along with BLE using the TimeSlot API. As part of this I need to set the Gazell mode to NRF_GZLL_MODE_SUSPEND while waiting for the next timeslot.

I've adapted the examples from the nRF51, and it looks like I have one problem to solve before it will work.

The problem is that whenever I use 

nrf_gzll_set_mode(NRF_GZLL_MODE_SUSPEND);
The call does not return error, but the mode does not change to suspend mode, and always remains 0 (device mode).
Also I never get a nrf_gzll_mode_changed() callback when trying to change the mode.
Gazell is enabled at the time I try to change the mode.
Is there something else I need to do to be able to change Gazell mode?
SDK 15.0.0, SD S132, nRF52832
Thanks,
Brian
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