I’m not personally familiar with buffers, so I recommend this article to get the background info: Low Loss Headers, the Complete Guide! - HeatGeek. Generally want to avoid adding a buffer, but sometimes it is necessary.
Other’s have had success removing a buffer, or converting it to a 3-port buffer, or to a volumiser:
- A Heat Pump Experiment. | Protons for Breakfast
- System Volume
- Fitting heat meter to 4 port buffer set up
- Just a thought on bigger buffer tanks
Alternatively, you can try to balance the flow on both sides of the buffer as zones turn on and off, which could be done by monitoring the temperatures at the 4 ports:
Does the heatpump turn off when the consumption pump is off? Or does it keep running to maintain the temperature in the buffer tank?
There is one other LG Therma V listed on HeatpumpMonitor.org, which may be similar to yours.
12 kW, 200 m², fully insulated, mix of rads and UFH, no buffer. Might be a useful comparison.