S1 co-registration unusably slow over forest & coastal areas

I have some software to automatically co-register stacks of S1 data using the python API. It has been tested over many different parts of the world and in most instances works without problem. However, when I process a scene over an area where there are not a great deal of ‘features’ in the image (e.g. areas of tropical forest such as North Selangor or Palangkaraya) the co-registration (back geocoding) takes days just to do a few bursts of one image. Similarly, for some images on the coast (e.g. parts of the UK) where the bursts being co-registered have a reasonably sized percentage of sea contained within them, the co-registration is also unusably slow. This is also the case when I run the same process from the GUI.

Is this a known issue and are there any solutions to speed this up?

(I am using a Windows PC with 128GB of RAM and SNAP 8)

Thank you,