Technical Engine stalls when slowing down with A/C on a warm day

[Sweep165]

Fiat 500 1.2 Pop Star 2015 41000 miles
My daughters car intermittently stalls when approaching a round about or junction when the A/C is on.

I have been trying to find a solution for this problem for a while and have tried many tests.

Things I have tried
Fitted new battery, Fitted another throttle body and reset in MES, Mass flow sensor Reset in MES, Evaporator valve, Cam sensor and crank sensor again reset with MES, Coil pack replaced Less than 2000 miles ago spark plugs and air filter replaced, A/C gas removed and refilled to 500Grams, Timing belt replaced and aux belt 3800 miles ago. The fat earth know to rot has been replaced and was not corroded. I have also added an extra earth to the alternator mount bracket to chassis. No error codes at all. I have reset everything 4 times
The car runs perfect and tick over is constant and very smooth
I.E I had all spare parts to hand as the original engine had been badly over heated . I found a genuine 2014 1.2 with 28000 miles which I fitted and runs mint.

The car is stalling rather than cutting out.
On a warm day 20+oC and fan speed 3 A/C on, the air in car is nice and chilly but when approaching a junction to slow down and 2nd or 3rd gear is selected the revs can be seen to lower rapidly and engine stalls by the time clutch is released it is the wheels driving engine that starts car. Same conditions but a 13oC day car rarely stalls
I have monitored A/C pressure and on a 15oC day only gets to 140 PSI on a 20+oC day 170 180 PSI is seen but compressor never cuts in for more than 10 secs
Am I filling A/C with too much gas? Or is it something else
When stationary engine fan lowers A/C pressure and compressor cuts in and out also engine revs are 900 RPM no A/C on 700RPM.

I think it is luck when selecting a gear when traveling and the A/C compressor is on the engine stalls

I have seen on some older Fiat 500 MY2009 there was software for similar problems but I do not think this will apply to a 2015?
Screen shot of software attached if anyone else has same model/year car

 

[John202020]

First try, have a specialist ac company drain and refill the system, as a comparison my mazda 6 system has about 450g in the system? On a hot day the ac compressor can run continuously when stationary I'm tempted to say yours has too much in, that said the system should trip out if over pressure, that shouldn't cause the car to stall in theory, the fact you say am I filling it too much suggests you are unsure how much you've put in and the correct amount to use, sorry but have a specialist re gas the system then go from there?
Will the car cruise at say 80 for some time without issue?
You used the original engine ecu?