Shapefile to PostGIS using FME - Column has M dimension, geometry does not

I’m trying to insert a shapefile into PostGIS using FME but I always get an error saying:

ERROR: Column has M dimention but geometry does not
CONTEXT: PL/pgSQL function debug.trig_fonc_force_geom_3d() line 6 at assignment

If I inspect the features in FME Data Inspector, the geometry info for the existing data in postGIS looks the same as the shapefile data, i.e.:

IFMELine (2 Coordinates)
Closed           No
Measures (1)     <default_measure>
Coordinates (2)  Coordinate Dimension: 3
0                -3.432432, 40.23948723, 0, <0>
1                -3.238473, 40.42348234, 0, <0>

I have tried every combination of setting/removing Z and M values but it doesn’t make any difference. I’ve tried both Spatial Type options in the wirter (Geometry/Geography) – what can I do?

Note:
I’m inserting into an existing table containing geometry. When the table was empty I was able to use FME to insert one batch of data but now I’m getting this error.

CONTEXT: PL/pgSQL function debug.trig_fonc_force_geom_3d() line 6 at assignment