Can you test the car in the early morning to see if it then makes 1 bar ?

You will always see the performance drop off on a Cossie, when the outside temperature goes up

To try and offset hotter air temps, you may need to consider fitting a bigger intercooler aswell as water injection etc.

With regards to your actuator, well the spring may have gone weak. In which case you will need to swop it over to find out. (make sure you get a Genuine Garrett -31)