Maps plots take a very long time to plot

[ADCollard]

I am getting a strange behavior when I try to plot a single channel map of ATMS departures using eva.

The file is produced very quickly and can be displayed, e.g.,

-rw-r--r-- 1 Andrew.Collard da 376178 Jun 27 17:57 gsi_omb_map_atms_n21_Obs_Minus_Forecast_unadjusted_8_TA.png

but then seems to be being updated without seemingly actually changing its contents

-rw-r--r-- 1 Andrew.Collard da 376178 Jun 27 18:01 gsi_omb_map_atms_n21_Obs_Minus_Forecast_unadjusted_8_TA.png

Note how the file size is the same but the time is four minutes later.

The next plot was similar, but took 7 minutes:

-rw-r--r-- 1 Andrew.Collard da 333524 Jun 27 18:08 gsi_omb_map_atms_n20_Obs_Minus_Forecast_unadjusted_8_TA.png

The YAML to produce this plot is /scratch1/NCEPDEV/da/Andrew.Collard/eva/eva_atms_n21_maps_ta.yaml on Hera.

Is this expected behavior?