Class AB Amplifier - Weird oscilloscope output
Quantization steps are visible in the waveform. The amplifier can't generate those, so they either come from the (presumably digital) signal generator, or from the scope analog to digital converter.
However... If the quantization steps were from the scope ADC not having enough bits, then the sloped top would be flat and horizontal: it would be a single quantization level. If we're seeing ADC quantization, then the signal as displayed has values between quantization steps, which is not possible.
So, the sloped top happened after the quantization that creates the visible steps. This means either:
1- The quantization steps come from the signal generator (probe signal generator output to investigate)
2- The quantization steps come from the ADC, but some sort of digital processing is applied to the data after conversion, which gives this abnormal result.
In both cases, this is a measurement problem, and your amp is most likely not to blame.