Looking at the route it seems allright to me. PFPX can't validate it, as the validation is done in IFPS (Eurocontrol), which only covers Europe. Trying to validate it returns the error (R)Route152: Flight not applicable to IFPS.
I'm not aware of a tool like IFPS for other continents, though the US have published a preffered routes document covering USA, which can be used to valid routes.
I'm usually not flying outside Europe and North America. But one way of validating routes could be looking at the AIP for the appropiate country.
The Thai AIP can be found at https://ais.caat.or.th/
The Malaysia AIP at http://aip.dca.gov.my/aip/eAIP/history-en-MS.html
and Singapore at https://fpl-1.caasaim.gov.sg/eaip.html
I've looked them thru, but haven't found anything indicating that your route should be invalid.
So I think that my colleges are right, when they point to the FSX/P3D database.
I'll try loading it into my system, if I can find time to test it.