The decawave chip uses a 40 bit long internal clock running with a period of ~16ps.
This means that the internal clocks wrap around roughly every 16 seconds.
The half period delay warning indicates that you have scheduled something to happen at a time more than half of this period away (i.e. 8 seconds in the future or more)
The most common cause of this is trying to schedule something for a time which has just happened because your processing took longer than expected and you’ve just missed the time you wanted.
I’ve also seen it caused by attempting to schedule a Tx a fixed time after an invalid Rx timestamp.
Sometimes the leading edge detection and correction goes wrong and you get what looks like a valid Rx but the corrected time is junk. If you then schedule a Tx for a fixed time after this reception you end up locking up for up to 16 seconds waiting for the correct time to roll around. One sanity check I found handy was to compare the Rx Timestamp with the raw Rx timestamp. They should be roughly the same but when this happens the two times are completely different.