Is this (still) a supported configuration for MLAT? Mine has started throwing this warning when I feed two dongles from the same remote Pi into a local dump1090:
11/03/2017 21:51:58 mlat-client(23251): Warning: the timestamps provided by your receiver do not seem to be self-consistent. This can happen if you feed data from multiple receivers to a single mlat-client, which is not supported; use a separate mlat-client for each receiver.