Recently I’ve been adding local bus routes in Ipoh. The bus routes are tagged according to PTv2, the bus stops should arranged in order as the buses stop, and the roads should arranged in order as the buses go, so that the relation is valid.
There are always some problems that make the bus route become invalid, such as when someone add turn restrictions, then the road might split and it messes up the order of roads unintentionally. (especially at two way roads and cross-loop routes)
We can check whether the route is valid or not at https://tools.geofabrik.de/osmi/ , but make sure to add public_transport:version=2 to the relation so that it will appear on the map.
In Kuala Lumpur there are some bus route without public_transport:version=2 tag, and some are incomplete and outdated (route numbers with “U” as prefix are not used).
Penang and Johor Bahru also have some bus routes, but most of them without the public_transport:version=2 tag, I’m not sure about the details but some seems to be incomplete.