Daikin erq250a7w1b freezing liquid line on heating

Hi

Can anyone suggest a reason for my liquid line freezing on heating

I have 3x Daikin erq250 connected to a air handler, 2 of which work ok but the 3rd which is running the top of the coil on the ahu is freezing down the liquid line, pressure drops to 3 bar -20 on liquid and the hot gas line is at 15bar so there is no heat at the ahu. I have recovered the refrigerant which was exactly the correct charge.

Any help would be appreciated

Many thanks