Make Synchronize Time of all Related items respect time remapping
When a precomp is time remapped, this setting is not respected.
David Simons (Adobe) commented
Because Time Remapping allows time to go both forwards and backwards, when moving "downstream" (i.e. from one to comp to another comp that has the first comp as a layer) there is not necessarily a one-to-one mapping of times, so there's no right answer as to what frame it should move to. This isn't a problem when going "upstream", and indeed AE does still synchronize in that direction even when Time Remapping is enabled.
But in cases that actually are one-to-one, like when time has only been slowed down but not reversed, AE could do what you want here even for the downstream situations. And for the non-one-to-one cases, it could arbitrarily choose one of the matching times at least.