Same thing as commit cf692c40
which was removed due to shutdown freezes.
Error thread is no longer there so doesn't cause any race sonditions,
was not able to repro any issues so will ask QA to test shutdown

There is still a chance user will try to move multiple landmarks one after another, but if it didn't update in the time user moves landmarks it's going to end up out of order either way

following promotion of DRTVWR-580

SL-19966 Reverted "SL-18721: Faster viewer shutdown time since performance improvements can lead to perceived inventory loss due to cache corruption"

This reverts commit cf692c40.