What happened to my performance

[Lord Mashie]

I let the plane climb to cruising altitude and leave.

I come back and the plane is at cruising altitude but on the verge of stalling from low airspeed. 

The attached video is after I descended a bit to claw back some speed but it does not want to climb back up even with TOGA thrust.

 

[Pilot061]

Look at the TAT and ISA temperatures - the engines think it is ISA +49 and are performing accordingly.

[Lord Mashie]

1 hour ago, Pilot061 said:

Look at the TAT and ISA temperatures - the engines think it is ISA +49 and are performing accordingly.

Oh wow that is very interesting. Don't know how it would think that

[Xenon341]

Yeah that's a MSFS bug with Live Weather.
You can switch to a preset weather then back to live weather and check if ISA temperatures are at normal level again