A318 - Baby Bus difficulties climbing

Hi Y’all,
So- I really like the A318 (aka baby bus), however, I seem to have an issue climbing up to let’s just say FL20. Essentially, in about 15,000- it struggles to climb and will stop climbing.
I have tried climbing in manual/autopilot mode with no success.
If someone can chime in on this issue that would be great,

Thanks.

Try to not have it fully laden.

Are you using managed mode? Make sure the auto throttle is engaged and the throttles set to the “CLIMB” detent. And disable any assists. I regularly fly above FL300 with no problem.

I’ve noticed problems with 1 engine shutting off while in flight, this will cause the plane to stop climbing. Have to to manual restart the engine. Not sure why this is happening but not fully familiar with Jets……I use the automated checklist to get up and running, that might be causing issues with 3rd party Airbus aircraft like the 318/319