Merge-Multilook-Terrain Correction processing doesn't end

Dear All,
I’m facing a problem during a Sentinel-1 SLC pair processing.
The problem occurs when Merge-Multilook-Terrain Correction (see attached graph file sigma_merge_ml_tc.xml (5.1 KB) )
is applied.
Input of this graph are the 3 complete subswaths of SLC pairs already pre-processed with Apply Orbit-Calibration-Back Geocoding-Enhanced Spectral Diversity-Debursting.
The same graph with the same multilook factors (48 for Range, 12 for Azimuth) works fine if in input are provided the coherences instead of the amplitudes.
The same graph with amplitudes in input works fine if multilook factors are changed (tests performed with 4 Rg and 1 Az, also with 8 Rg and 2 Az) .
If the attached graph is run the processing never ends (I waited 3 days before killing the processing), like an infinite loop.
Can someone help me on this?
Is the amount of RAM (-Xmx24576m in my case) not enough when the multilook factor increases over a certain limit?

I would recommend to subset the images right after the Applying Orbit file step. In my case (16GB RAM) almost any operation on the whole SLC images wasn’t possible.