NaN in output


I have been looking at some model output and I am seeing a nan in some of my data fields at certain months of the year in certain grid cells. When I look on the map, this is a white square in the field:
Screenshot at 2023-10-04 15-03-04
This doesn’t seem to have happened in earlier versions of this branch (vn11.1_h2_emissions_ch4_lbc_lat) before I had merged in two branches at revision 117556 and 117552.
Any thoughts would be very appreciated!