I can no find evidence that these companies have a specific policy about Kashmir in particular, but the enforcement of their community standards have been perceived as censorship on multiple occasions.
Here is an article on the Guardian from 2016 where several users describe Facebook account terminations which those users felt were not justified. In some cases, Facebook has apologized for and reversed these decisions. But in general, Facebook issued a statement defending these actions as follows:
“There is no place on Facebook for content that praises or supports terrorists, terrorists organisations or terrorism. We welcome discussion on these subjects but any terrorist content has to be clearly put in context which condemns these organisations and or their violent activities. Therefore, profiles and content supporting or praising Hizbul Mujahideen and Burhan Wani are removed as soon as they are reported to us. In this instance, some content was removed in error, but this has now been restored.”