I believe it was reported already but here is a save with moment when mass disappeared. Metal refinery requires 400kg of coolant - it was liquid steel. There was 406 kg of liquid steel in that loop one cycle earlier. However, now there is only 396kg. Where 10kg? Somehow liquid pump suck liquids twice but skipped releasing one pocket of liquid during saving process OR released pocket was not covered by save.
There is also save from next cycle WHEN I DID NOT LOADED THE GAME. There is 406kg in the loop!!! So it happens only during loading process.
I hope it helps You somehow.
Probably two liquids pump setup working while the game is doing its save.
Load the game of that save.