Hotpoint FZA34G freezing to -10°C

Hotpoint FZA34G 60cm under counter freezer

This seemed to start after the electricity was cut twice for maintenance

The freezer will not reach -18°C
Freezer works as normal down to -10°C
It maintains this temperature
Pressing fast freeze does not work
Compressor tries to start but fails

I changed the capacitor but no change

Tested the thermistors by pressing fast freeze when door is open and then closing it
All thermistors seem OK

Took panel off inside of freezer to check evaporator
No excessive ice and fan works

Any advice on where to go next would be appreciated,

Regards
Mark