fix 3/6 failures

astropy/utils/iers/iers.py

@@ -591,18 +591,25 @@ def _combine_a_b_columns(cls, iers_a):
         # after 'I', we can use searchsorted for 100 times speed up over
         # finding the first index where the flag equals 'P'.
         if hasattr(table["UT1Flag_A"], "mask"):
-            s1 = ~table["UT1Flag_A"].mask
+            mask = table["UT1Flag_A"].mask
+            s1 = ~mask
+            # a hacky way to get the position of first non-masked value
+            offset1 = np.searchsorted(s1, True)
         else:
             s1 = slice(None)
+            offset1 = 0
 
         if hasattr(table["PolPMFlag_A"], "mask"):
-            s2 = ~table["PolPMFlag_A"].mask
+            mask = table["PolPMFlag_A"].mask
+            s2 = ~mask
+            offset2 = np.searchsorted(s1, True)
         else:
             s2 = slice(None)
+            offset2 = 0
 
         p_index = min(
-            np.searchsorted(table["UT1Flag_A"][s1], "P"),
-            np.searchsorted(table["PolPMFlag_A"][s2], "P"),
+            offset1 + np.searchsorted(table["UT1Flag_A"][s1], "P"),
+            offset2 + np.searchsorted(table["PolPMFlag_A"][s2], "P"),
         )
         table.meta["predictive_index"] = p_index
         table.meta["predictive_mjd"] = table["MJD"][p_index].value