I got the following severe error during the sizing run.

   ** Severe  ** Plant flows do not resolve -- splitter inlet flow does not match mixer outlet flow 
   **   ~~~   **  Environment=WINTERESIGNDAY HTG 99.6% CONDNS DB HVAC Sizing Pass 1, at Simulation time=01/21 05:00 - 06:00
   **   ~~~   ** PlantLoop name= CHWLOOP CHILLED WATER LOOP
   **   ~~~   ** Plant Connector:Mixer name= CHWLOOP CHW SUPPLY MIXER
   **   ~~~   ** Mixer outlet mass flow rate= 50.063643 {kg/s}
   **   ~~~   ** Plant Connector:Splitter name= CHWLOOP CHW SUPPLY SPLITTER
   **   ~~~   ** Splitter inlet mass flow rate= 1.417500E-002 {kg/s}
   **   ~~~   ** Difference in two mass flow rates= 50.049468 {kg/s}
   **  Fatal  ** CheckPlantMixerSplitterConsistency: Simulation terminated because of problems in plant flow resolver

Actually, I have already identified the cause of the severe error.

• Multiple variable chilled water primary pumps is the cause. One variable chilled water primary pump or multiple constant chilled water primary pumps does not cause the error.

  

• The error occued only in the large model. The maximum chilled water loop flow rate of the model is 3.42m3/s. I tried to reproduce the error with small models, but I couldn't.

• The presence or absence of bypass pipes are irrelevant to the error. I have tested.
• I found this post when I searched the word "CheckPlantMixerSplitterConsistency", but my case is irrelevant to EMS. The error also occured in the following hot water loop of another large model without EMS. The maximum hot water loop flow rate of the model is 1.16m3/s.

   ** Severe  ** Plant flows do not resolve -- splitter inlet flow does not match mixer outlet flow 
   **   ~~~   **  Environment=SUMMERDESIGNDAY CLG 1% CONDNS WB=>MDB HVAC Sizing Pass 1, at Simulation time=07/21 00:24 - 00:36
   **   ~~~   ** PlantLoop name= HWLOOP HOT WATER LOOP
   **   ~~~   ** Plant Connector:Mixer name= HWLOOP HW SUPPLY MIXER
   **   ~~~   ** Mixer outlet mass flow rate= 13.100580 {kg/s}
   **   ~~~   ** Plant Connector:Splitter name= HWLOOP HW SUPPLY SPLITTER
   **   ~~~   ** Splitter inlet mass flow rate= 5.837538E-004 {kg/s}
   **   ~~~   ** Difference in two mass flow rates= 13.099997 {kg/s}
   **  Fatal  ** CheckPlantMixerSplitterConsistency: Simulation terminated because of problems in plant flow resolver

I wonder if anyone else has experienced the same error. Is it a known bug? Is there a better solution than integrating variable primary pumps into one? The weird thing is that the error in the chilled water loop occurred on a winter design day, and the error in the hot water loop occurred on a summer design day. There may be a setting to avoid it, but I don't know. The error occured in V9-6-0 and V22-2-0. I'm sorry, but I can't share my idf files.