Thanks for the feedback. I don't have a 3597HD to reproduce your problem to debug the root cause. Could you give more details about your setup so others can reproduce? In particular,
Origin of the device: official Thailand device or from other country
Firmware: version and language
Map: version and language (dual or Thai only)
JCV: version, filename, resolution, is it created by GarminAsianJCVTool.exe?
Locations: coordinates of the locations where JCV does not work
Lastly and most importantly, keep everything the same except replacing the JCV file with the corresponding official unpatched JCV file and see if you get the same or different results. If different, can you upload your patched JCV file for debugging? Thanks.